problem communicating with bitcoin RPC, solo 4870x2 + Guiminer + Bitcoin 0.3.21

[dfn]

I need some help getting bitcoin to work. I am using Guiminer and Bitcoin 0.3.21 with a Radeon 4870x2.
Basically, I always get the RPC error ('problem communicating with bitcoin RPC') after 30-35 minutes of solo mining.

I start Guiminer, create 2 workers (one for each GPU), and start mining. After 30-35 minutes, I get the RPC error (I see it in the console of Guiminer). I have tried Bitcoin 0.3.24, but switched to 0.3.21 after searching and seeing someone recommend that for solo mining in reply to a poster getting the same error as I was. I have also made sure my config file allows all IPs, and I've basically "allowed" all for Bitcoin and Guiminer in my firewall. Just to be sure, I tried running them with my firewall off, and I still get the RPC error.

So, to summarize, I am getting the following error: 'problem communicating with bitcoin RPC'
I have tried the following:
-switching to Bitcoin 0.3.21
-enabling all IPs in config file
-allowing all in my firewall
-shutting down my firewall

I am running Bitcoin and Guiminer on the same machine, Windows 7 Enterprise x64 with a Radeon 4870x2. I'd appreciate any help with this, I don't know what else to try.

PS-I have the latest version of Catalyst drivers installed and OpenCL. I tried following a few different tutorials for setting up solo mining, but they didn't solve my RPC problem.

[hmblm1245]

A bit off topic the odds of finding a block with such little hash (compared to the bitcoin network hash) as a solo miner is very small. On that note try pooled mining and see if the same thing occurs. also, try disabling any antivirus protection or such.