I CAN'T BELIEVE IT!!!! I lost an entire day over this!!
OpenAccess doesn't update the app.config file with the scale of decimal fields when they are changed on sql server. Even after doing a merge of the schemas. This is a definite bug in your system i believe.
I've manually updated app.config on my system and it works fine. It was doing the equivalent of Decimal(9,20).
Could you please confirm if this is a bug or not, or just me not seeing something.