If a posting journal file exists, this will prevent other processes that require the journals to be purged from running. This includes Year End Processing and editing Control Account Sets. Likely the scenario is that though you chose to print/purge the adjustment audit list, something on the computer/network was holding on to it and prevented it from setting the file size to zero.
To fix this, you need to manually rename or delete the file. In the data directory, look for files that start with 'ARPOST' - for example, the adjustment posting journal is 'ARPOSTA.dat'. Make sure no-one is in the data, and rename the extension to 'old' or something other than what you are using. If there are any other 'ARPOST' files that have a size greater than zero, follow the same process.
This should allow you to edit your control account set. Also, these renamed files will be recreated the next time you post a transaction.