I've tried this a couple different ways, using ExecuteCode() and
Compile() but can't seem to get it to work.

I have a block of dynamic code stored in a string variable, and part of
that code calls ChangeSourceWIndow() for one of my internal window frames.

However when the program reaches that code, it errors out with
"InternalWIndowName" element unknown.

Is there something special I have to do to make this work? (if it's even
possible)

I guess i could resort to creating some global flag variables and
changing them inside of the dynamic code instead of calling
ChangeSourceWindow() directly.