Hi John,

Thanks for your prompt response.
Actually, I found another question on the website with a similar problem
that I hadn't found with an earlier search, and tried that solution and it
worked. For the benefit of others who might read this, the problem did seem
to be one of overflow (900,000 rows). The advice was to compact and repair
the database, then open a blank database and link to the source table, and
try again. I lost my work on my query (which had a few calculated fiels and
expressions) but it was worth it to get going again.

Again, thanks. You guys are just marvellous.

Matilda