Add-in closes SolidWorks

Hi there,
I have created an add-in, but on some PC's when you load the add-init closes SolidWorks. When you go to Tools/add-ins it is notlisted.

The add-in does work on some PC's (same setup i.e., same OS andservice packs and SW SP) so I am not sure what could be causing theproblem

If you have experienced similar problems or have have any ideas,please let me know.
Thanks

SolidworksApi macros