First, you should only need to add the $Conf{RsyncBackupPCPath} setting to the main config file.
It's likely that that $Conf{RsyncClientPath} is not set correctly based on the old $Conf{RsyncClientCmd} setting. What are those settings?
You should look in one of the failed backup XferLOG.bad file. Please email the first few dozen lines (up to and including the error), assuming it is not too long.
Craig