Likely that somewhere, code references a specific version of an Office program that is no longer valid. One example would be the TransferSpreadsheet method where acSpreadsheetType8 (Excel 97) is specified. Not saying this is the exact reason, it's just an example. If you can open the vb editor and set the property to break on all errors you can try to discover which lines of code trigger errors. There are no references in the affected project that are tagged as 'missing'?
The more we hear silence, the more we begin to think about our value in this universe.
Paraphrase of Professor Brian Cox.