MultiBit Decrypt Issue

Hi there, in March I backed away my MultiBit wallet for later use... I backed up several copies in and around that time (I've been very busy and away from the crypto scene). Yesterday, I installed MultiBit again and dragged my original (backed up) MultiBit roaming folder into my new Windows installation, which included the ".wallet", ".info" and "wallet-data" folder, I loaded the wallet up, it sync'd happily.

I've just put in my password and it says it can not decrypt bytes to change/remove the password? When I go to export my private keys it says the same thing.

I know for well it's the right wallet password when entered (I checked twice when, and double checked in march when I changed the wallet password to the more advanced one), I copy paste it from a txt document that I un-encrypted each time with a master password instead of writing it out by hand, It was working like this and now it is not.

I've tried installing MultiBit on my laptop and doing the same process. No luck. I tried importing the only private key I had from January, it won't open or accept my original password, comes up with the decrypt bytes message again...

Please help.