2003 file with 2007 error "the file does not exist our you do not.

I have a db developed in 2003 and I put it on the blackboard website for
everyone to use. Those with Office 2003 can open it and use it. Those with
2007 get the error : "the file does not exist or you do not have read access
to the file."
I went to the trust center and tried to make it a trusted location but that
did not help. It seems like a security issue, but I don't know how to
correct it. I checked Internet Explorer security too but wasn't able to find
anything.

Kathy