You have placed your file in a directory where only Admin users can modify the file. Right click this directory and change the directory's security settings to allow the other users to have "modify" rights on the directory contents.
Thanks for your quick reply, Phil.
I thought that might be the problem, but the IT person who set up the computers for me assured me that the file and folder permissions were not the problem and that it had to be something within FMP 11 since the title of the error message was "FileMaker Pro". Also, when I tried to modify the folder permissions on the system, I wasn't seeing a Security tab in Folder Properties. Our IT person said this was because there were no restrictions. Well, it turns out that she was mistaken. I now know that you can't set individual file and folder permissions in XP unless you turn off simple file sharing in My Computer, Tools, Folder Options, View tab (the default value on XP systems). Once I turned that off, I was able to give users modify and write permissions. Before that, since the folder in which I stored the FMP data file was created using the Administrator login, only that login and users assigned to the Administrators group could modify the file. Yeesh!