This error usually occurs because on the Nominal tab of that transaction a line is using an invalid subanalysis code or perhaps is not using one at all.
To resolve this:
On the transaction, right-click and select Modify mode.
Change the Subanalysis code manually. However, if this is not possible it may require one or two other fixes.
New subanalysis code
Set up a new Subanalysis code to match the incorrect one used in the transaction. When authorising the transactions, it will look up the Subanalysis list and if it finds a match, it will validate and no longer produce this error.