TrueGrid 7, running under VB6 was coming up with this error. As it turned out, we had a
droplist powered by an ADO data control. This data control's recordsource was being
changed from looking at table1 to table2 and back.
That is, in one event it had dta1.Recordsource = "Select field1, field2 from table1" and in
another it was selecting from table2.
In a later incident, we found we were assigning to a TrueGrid column's Value property,
not its Text property. The Text property seems more forgiving of formatting junk ... or
something. Changing to Text solved that one.
Don't know if that would be the same problem you are having, but I hope this is some help
in solving it.