In the Scale Charges wizard the following message may appear even if you haven't ran it for that period:
'The scale charges for this month has already been posted. Are you sure you wish to continue?'.
NOTE: We've resolved this issue in v33.0 and above of Sage 50 Accounts. If you aren't using the latest version, upgrade now. If you're unable to upgrade, as a workaround, click Yes to continue and post the charges.