I should have added the following as it may be relevant:

I create a program in a machine with Excel 2007 and move it to a machine with Excel 2010.

I open it in 2010 and 4 modules do not load correctly.

From within 2010, I remove each of these 4 modules and import replacement bas modules.

I save and close the program and thereafter it works perfectly in 2010, on this and other machines with 2010.

I move it back to 2007 and these same 4 modules will not load.

thanks