Hi Garrett,
found some time to dig today and wanted to follow up and tell you the latest findings, still without a conclusion thou.

The necessary sample still more simplified:
Form: two textboxes in a container, controlSource="dsbld(1)" and (2)

VFP8: Error 45 in command oFrm1.Show - Not a character expression

I removed controlSource from the textboxes, just to be sure this really throws the exception, and yes, it does.

As this is legacy from the early 90s, things are quite convoluted. So I traced and...
- The global array is declared and initialized as C in the main PRG way before any form is instantiated - and it is never reDIMEd...

The error error (no typo <g>) must come from the order objects are defined and CLASSLIBs are SET ADDITIVE.

Hope I can really nail this when I find time for an example.
Thanks for listening
G