Excel 2007 Unprotect Sheet prompt in password protected sheets on Windows 7 machines

Windows 7 users of software I created in Excel get an "Unprotect Sheet" prompt when clicking on any sheet or cell in a sheet that is password protected. They hit cancel, sometimes several times and the Unprotect Sheet dialog box prompt goes away. Only to reappear when clicking on another sheet. The users had no problem with the file until they upgraded their computer to a Windows 7 machine. Could there be something in the VBA project macros related to setting protection on the sheets that could be offending Windows 7? Is there a known bug in Windows 7 with how it interacts with Excel files with VBA projects or password protected sheets? This has become very frustrating having to deal with the Unprotect Sheet prompts.