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The error message "could not convert variant of type null into type
string" appears on a number of
forums and newsgroups. Usually it relates to ADO connections to
databases, usually using TTable type components, and usually the error
only appears at design time.

I have an application that is generating this exception. It generates
it in a production environment, which I have as yet been unable to
duplicate. The application is using Interbase Express components,
which I believe (rightly or wrongly) don't use ADO. My application has
no TTable or similar components whatsoever, only TIBQuery, and
TIBDatasets.

The user feedback tells me that user A adds a record to dataset 1,
then user B selects a menu option to update a list box from dataset 1,
when user B attempts to add a record to a different recordset (dataset
2) he receives the above error message. No data from dataset 1 is used
when creating the record in dataset 2. Once user B restarts his
application the error is not seen again (so no problems with the
actual data).

As yet I have been unable to replicate this in a test environment.
Rather fuzzy I know, but does anybody have any ideas about what is
happening.

Any help will be gratefully received. I'm totally at a loss to explain
it!