Hi Dana

if you want to post to i.e. default 2100 account payable account, you need check Maintenance, Data integrity first, see if Account payable and unpaid invoice is being inconsistent first. (2100 it is a control link account, you can not just post to it, unless you have accountant's edition version)

If you do have in data inconsistency issue with A/P and you do not use foreign currency, you can go to Link Account and unlink accounts payable and then post adjusting entry and Link it back then check Maintenance, Data integrity see if it is fix.

If you do not have data inconsistency issues I would not recommend you unlink it, as you will create incontinence issue by doing that 

i assume 'cra-gst' is a vendor
create purchase invoice to 'cra gst'
  invoice # is the year end entry #
  date is the year end date
  amount is -1111.00
  no tax
  account is 'retained earnings previous year'

control J will show the entry that will be created when you post