> The solution is for the SysCancelAll to have a try-catch block which
> handles the AV and continues on its merry-way cancelling other
> Datasets. I will try and see if this solution works (although I work
> in BCB and adding .pas files to my project doesn't always work).

I strongly suggest that you allocate/remove your dataset outside the
transaction context - and certainly DONT allocate/remove inside other
transaction event processing.

Explanation: So there are some instances where you cant (or should
not) do certain things inside events - since that would violate the
status of loops etc when the processing returns to the outer call.
I hope that makes sense, its a bit hard to explain without lots of
code for demo.

While I have not investigated I would expect that this is what you
are encountering. You need to find a way to perform your query
allocation/deletion outside of IBO transaction event processing.

--
Geoff Worboys
Telesis Computing