When I add a line of code or take away a line of code in one of the banked modules the program takes 23 seconds to start. It doesn't seem to matter what code is added or where in the module. It also doesn't seem to matter what code is removed to create the same symptom.
I think it some sort of linker issue, but don't quite understand how to troubleshoot.
Thanks for the suggestions, I did carefully check the hardware memory mapping, so I think that is ok.
I wasn't the original author of the code, so while the ISR's are in the common block I haven't checked whether they call something outside the common block. I'll check that (Thanks!).
Thanks for the string constants warning.