This is an old post, but no one has explained what’s happening and I made a previous post which did not lead to the resolution. Epicor is adding a lot of extra fields within the external report dll as part of the other referenced system tables which do not have any field exclusions visible to the user.
As a huge disclaimer, I did not perform any verification that these are not used in normal calculations, so I can’t recommend you modify these. However, if you were to remove these tables which may or may not be linked to CSF for Mexico (for instance by deleting from the Report Table list view), it will drastically reduce your RptLabel column count to under 1024 columns.