Symantic Norton AntiVirus has been know to cause Excel 2007 to crash when running Paymee, especially on Windows XP. As a reference refer to Microsoft Article: http://support.microsoft.com/kb/329820
This issue is not specific to Paymee - the crashes occur for many locked Excel Addins such as Paymee.
If your Excel frequently crashes & you have Symantic Norton AV, we recommend running Norton 'Live Update' to be sure you have the latest Norton AntiVirus patches for scanning MS Office files. The instructions for running Live Update varies depending on your Norton AV version. Typically, launch Norton via Windows Start Button -> All Programs -> Norton AntiVirus (also know as: Norton Internet Security). Then select 'Run LiveUpdate' from the resulting dialog or from within the Norton Options.
If Live Update does not address the issue, then try disabling Norton AntiVirus from scanning MS Office files. This will also speed-up Excel.
To do this launch Norton AntiVirus & uncheck "Turn on scanning for Microsoft Office Documents"...
To open the above dialog from Norton Internet Security (varies) refer to Virus & Spyware Protection Options...
If your concerned with potentialaly running unsafe Office files, we recommend setting the Excel 2007 Macro Security settings to "Disable all macros except digitally signed".
In this way Paymee will run (Paymee is digitally signed) & you will still be protected from acidentally running potential malicous code. For more info on Excel 2007 Security settings se here.