SQL problem - joins plus sub query (Paradox7)

D2.0, C/S, W95
Is there a problem or an SQL limitation when trying to select from two
tables with a join, and also use a subquery?
For example, I'm using 3 tables: Company,  Contacts and internal contacts
(both the two contacts tables relate to the company table).

Company
-------
CoID
CoName

Contact
-------
CXID
CXCoFK          (foreign key to company table)
CXName

IntCont
-------
ICID
ICCoFK          (foreign key to company table)
ICStaff         (Staff Number)

The query I want is all companies who have a contact called Joe AND whose
internal contact (eg account manager) is Fred (who is person 2 in a staff
table).
This gives a query such as:
select CompanyID, CompanyName, ContactName from Company, Contacts
where CXCoFK=CoID and CXName='Joe'
and CoID in (select ICCoFK from IntCont where ICStaff=2)

This doesn't give an error but ingores the subquery, even if I change the
last line to
and CoID in (12)
(which should return a maximum of one row, but it shows all the Joes).

BTW, if I use the same subquery against a single table (no join) then it
works fine, eg
Select CoName from Company where CoID in (select ICCoFK from IntCont
where ICStaff=2)

Any idea why this happens, or can you suggest a workaround?

Please could you email a reply as well, as I don't always have access to
the newsgroup.
Thanks, David Carle