#1. are there any characters on a keyboard that are not accepted into a passphrase?
Not as far as I know, but I suppose I might be misinformed about that.
#2 I had a clean up of some files only computer cos was a lot of wasted space on my disk and was fairly sure of what the folders were, but could somehow the file that had the passphrase in it have been deleted and this is why it won't accept?
There is no file containing the passphrase. The passphrase is used to encrypt your private keys. If you supply the correct passphrase, then the software will be able to decrypt using that passphrase. If you don't provide the correct passphrase, then the software will fail when it attempts to use the passphrase to decrypt. As long as you are seeing your receiving addresses and correct balance in the wallet, you have not deleted the file that contains the encrypted private keys. It sounds like you may have made a typo when creating the passphrase. If that is true, you'll have to figure out what typo you made to reproduce the same passphrase.
I have backup files of the wallet.dat still
And had backed it up before any coins went in and again after coins went in,
Was the backup created before or after you created the passphrase?
#3 is there a way to work around this somehow??
If the backup was created before you created the passphrase, and you have not sent any bitcoins or created any new receiving addresses after creating the passphrase, then you can recover the backup and access your bitcoins.
Otherwise, you'll have to keep guessing until you get the passphrase correct. There are some common mistakes that you can try such as leaving "Caps Lock" turned on, or hitting the shift key one character too soon, or releasing the shift key one character too late, or hitting an adjacent key on the keyboard, or using copy/paste and accidentally failing to include the first character (or first few characters) or last character (or last few characters) in the selection.
There are some individuals who have posted programs in the forum that will try many variations of your password for you to figure out what the correct password is.