It seems there are posted entries for which this dimension value is not specified, one of the possible reason can be that earlier “Value Posting” for this account was
not “Code Mandatory”.
If I were to resolve this issue, then I will turn debugger ON and see which entry is throwing this error and act accordingly.
You may perhaps have to modify (using C/AL Code) the Ledger Entries (If it is a global dimension).
PS: It is strongly recommended to not to change the ledger entries, it may be illegal in some countries.
Now when you already have postings done, quickest way to find out line(s) causing error is as Dhan suggested - use debbuger and examine at what records (lines) it stops, then with Developers access you can insert the missing Dim values.
OR - temporarily turn off CodeMandatory for G/L Acc in question - this will allow you to run batch job, BUT THEN in some G/L entries Dims will be missing.
After you find out where the Dims were missing, you should put the Mandatory-ness of them one level up, because now you have a situation, where SO/PO/something else is allowed to be posted without these Dim(s), but these same Dim(s) are mandatory on G/L level. So, further on nothing can be posted with unentered necessary Dims.