Thank you for your post.
Have one of the clients with full privileges pull down the File menu and select "Manage -> Database...". Click on the Relationships tab, and make sure the two files are related to one another. It appears that the relationship has broken and needs to be reset. Once corrected, see if the drop down list now responds properly.
They did send me screen shots which shows that they have the files in a subfolder inside the Databases folder. Could this be the issue?
That's very likely the issue. A great many external file references in filemaker locate a file in relation to the location of the directory that holds the first file. If they have it in a different directory with a different name than what you used to create the database, many such references will break.
TSGal's directions will fix that for you for this instance, you might have other broken relationships.
Thanks! That worked. :)