10/24 firmware seems better for most S3's ... but some people are still flashing the latter firmwares (though I'd advise against that).
Interesting that you are all in with solo mining .... for how long have you been at it any luck? I am contemplating on pointing a couple of mine there .... but the thought of going forever without any rewards scares me, for now.

The saying goes, if it ain't broke, don't fix it!
So it depends where you are at;
1. Does the new firmware work for you? Then what are you trying to fix?
2. I doubt the new firmware is working better for you, but you should know better since you have your rig, in which case I'd be tempted to revert to the older one .... a simple reset should do it, or you can reflash if that does not work.

you should be invoking vi editor by typing:

The latest firmware (since Oct 2014) is crap on many levels, but that is a sidenote. For a start, I'd desist from changing voltages on that as the default setting of 0000 seems to find its sweet spot, and to add to that (and as you realised) it seems when you set a voltage with the newer firmware, you consistently loose hashrate and have to restart cgminer to recover it. In my opinion, not worth it! If you have the Oct firmware, reflash your rig (a user also posted one here)

Never come accross the permission denied error on an S3 ... are you logging in via SSH as root?

That's interesting. I wonder why my S3 displays a best share while mining on slush but never displays one (i.e shows 0) when mining on ghash. It is the same S3, and I assume using the same driver .... or does cgminer change the driver change according to the pool you point it to?
EDIT: Or is it that the difficulty at ghash is always a power of 2 value (not sure what that means ....) and at slush is never that?

Are you sure you just rebooted?
I had a similar screen when I tried to run cgminer 4.6.1 on an S1 but forgot to modify the soft link to point to the new binary. I am not saying that is what you did, but clearly your cgminer is NOT starting .... try doing it manually (first stop then start) via the UI. If that fails, SSH into the rig and type cgminer-api then enter and post here the response you get.

There definitely is a correlation between HW % and rejects. Furthermore, rejects reduce shares thus rewards if you are mining on a pool, and if solo mining redue your chances of solving the block even further.

Best share does not work on some pools (e.g ghash) , but works on others (e.g slush), so it is incorrect to say it has never worked, more like it does not work on your pool.

EDIT:
Diff settings can help improve rewards when mining on a pool in the very short run, so it may be fair to say it is not an issue on S3's, but that depends on the pool you are mining on. Some pools take an age to set a var diff thus costing you rewards, while others are quick. Also, intermitent connections can result in the pool setting a low diff that reduces rewards, so there is no harm in setting a minimum diff for the S3 at the onset. In any case, if the pool detects the rig is hashing at a higher diff than you've set, it will adjust it accordingly.
END EDIT:

PS. If you are not sure of the answer, do not clog the thread with waffle.

^^^ Clear as mud .....

No, bitcoin luck is computed as a factor of the probability of finding a block given your (the pool's) hashing power and the network hashing power, given that the number of blocks that can be released by the network in the effective timeframe is known.

In our case (and this is a conspiracy theory of some magnitude!), I am thinking the new hardware that hit the market of late, ahem... S5 ... have not been deployed en-masse on slush, but elsewhere, and that is reducing their luck thus we pick up the pieces where we were beaten by a matter of seconds before! Of-course, that theory assumes there is something wrong with the S5's (even the S3 variants and other bitmain rigs updated with the Jan firmware!).

Anoother one!

It is a strange firmware that of Dec 16th.
Go to Miner Configuration => Advaned Settings then Save & Apply and it should hash well after that (I have not tried to but stopping and starting cgminer could also work).
Basically, another fudged firmware ....

So, if you're not sure then let someone else help.

Would be nice if you took your own advice, most of the time. Saying that, this is a public forum that anyone is free to give advice as they see fit.

In any case, last I checked it seemed like the problem was due to the pool, so your advice to open up the the rig may be, to put it politely, another wild goose chase, aka useless afterall! (EDIT: Or should I have said, if you're not sure then let someone else help.)

Go ahead and buy one and the manner you'll be charged VAT / import duty is dependent on the carrier you use.

1. DHL - They'll notify you of the duty due + their handling charges as soon as they get the unit and you can pay via debit / credit card before delivery. In my experience, I paid the invoice on the day I got the notification and received the unit in 2 days.

2. UPS - Just wait for your delivery and have ready at hand either cash (drivers don't like this), a cheque or a debit /credit card to pay your duties + their charges. For the latter, the driver will give you a number to call and make payment. You will be notified of the charges when the delivery reaches your door and only after payment is completed will you get your unit. In my experience, the unit took 5 days.

3. EMS - I have no personal experience from these guys as they have just been re-added for the S5, but I have heard stories that they sometimes "forget" to charge import duties and therefore no handling charges, but I'd err on the side of a UPS'esq service.

Hmm ... check your logs, both the system log and the kernel log. you can also try stopping then starting cgminer then check the logs.

I admire you for running an antic firmware! But yeah, if it ain't broke, don't fix it! Nevertheless, you may do better with the December 19th firmware ... at your risk.

Go to Network tab then click edit on your connection then switch the protocol to DHCP and Save & Apply.
You'll get a new IP address, so it will not be on 192.168.1.99 anymore, but will begin hashing straight away.

Quick, clean and easy fan muffing for the those that have an S3+.
Swap the push fan from an S3+ with the stock S5 fan. At 3500 rpm, the S3+ fan hums (or purrs) whereas the stock S5 fan whines ..
On the orher hand, the stock S5 fan will run at a much lower rpm when strapped onto an S3, thus won't be as loud as when it is on an S5.

Your S3's shipped with the "faulty" firmware so you will have to flash them to the latest 19th December firmware.
To check what firmware you have on your S3's, go to the webUI Status => Overview page.

Get the latest firmware from the bitmain support page.

Replacing out the metalic cover with a plastic /perspex one sure saves weight, but how much weight would a plastic / perspex top and bottom add to the overall weight of the S5? (rhetorical question so you don't have to answer 'cause I know it is insignificant)

Actually, I think bitmain got this a bit wrong, but the good thing with them is that they listen to ideas (and test them out).

In the shape the S5 ships, it is NOT very well suited to home mining, but then again they had to be competitive pricewise so I think they tried to gain efficiencies with the cooling system they deployed on the S5 and by reducing weight and components, but ended up with a product that is neither well suited to home mining nor very well suited to commercial mining (the latter due to its lack of stack-ability!).

Having said that, the S5 can be made a lot quieter by replacing the stock fan with a quieter PWM one OR reducing the voltage to the stock fan with a resistor; you'll then need to add a second pull fan, and possibly have the top and bottom closed off.
Come to think about it, bitmain could engage a partner (similar to their liquid cooling one) to offer S5 to home upgrade / downgrade kits (whatever that qualifies as) after testing that include a pair of quiter fans + top / bottom covers (Not really worried about the covers as I can use card-board). Of-course, that depends on the longevity of the product line.