The problem could be a number of possible things.

You could have malware which is messing with the clipboard and resulting in bad text being copied and pasted. In this case, you should perform a malware scan on your computer.

Your wallet file could also be corrupted so the passphrase no longer works (and also the private keys are corrupted so you may not even be able to access your Bitcoin). In this case, you should restore a backup of your wallet file (of course back up the wallet file first to another location, then restore a different, older backup) and trying to see if that works too.