Object inspector can't find field

I have much trouble with a table in an Access database (lets call it
TableA). It has just one field, it is used to filter the main table.
Users enter the list of data they want the database to be filtered on.
Program then sets the database's main table (let's call it TableMain)
Master Source to dstableA, and the Master Field to TableA's field (an

I often had ?Non blob field required? errors when assigning the Master
field at run time.

A TDBGrid is available to modify TableA's data. In the IDE, the Grid's
object inspector finds the Data source, but can't find the field in the
table, although table is active.

I am using Delphi 5 professional, Win ME, 128 Megs of RAM; using ODBC
with Access 2000 database, BDE 5.10.

Can you help me? I've been on this for a week!