Welcome to the abiguity of the relational setup.....I am by no means an expert in this area of Access....
What I usually do to try to solve the problem is take a look at the realtionships window. Is everything setup correctly there. That being correct, I go back to the query. If the relationships are set in the realtionship window, the relationships you see in the query are "inherited", and can be modified but won't affect the "main" relationships. So begin by removing one. See if you can modify. Put it back and remove another. Go thorugh all the steps....next remvoing two at a time, etc.
Somewhere, one (or more) of those defined relationships just don't work....Sorry I can't give you a definitive answer on this....I might suggest reposting this new problem in the Tables/Relationships or even the Other Forum for someone else to help you out more than I can....Just be sure to include all the steps you have already gone through in order to for the person assisting you to better help and not duplicate previous work.... Please remember to give helpful posts the stars they deserve!
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Robert L. Johnson III, A+, Network+, MCP
Access Developer/Programmer
robert.l.johnson.iii@citigroup.com