I had this error since I have migrated from FRX.
The error was a general error "An unknown error has occurred"
Went to configuration console the I have found "System.OverflowException: Value was either too large or too small for a Decimal."
Solution:
It was the format. I had a custom format for the percent, at the column level. Change any custom format to their standard, in this case percent. Then like magic everything worked just fine.
I hope this helps because I looked all over the net for a solution and it looks like nobody have had this issue before.
