Pete said:
I have taken on a db (previous author not unavailable)
where this button is disabled - so the question still
stands...
If the design button is disabled it's likely because you have an MDE file
where design of code-based objects is not possible. The file extension
need not actually be "mde" in this case.
Is the button also disabled when you look at the tables and queries? MDEs
do not prevent design changes to these objects so if the button still works
for those then it is almost a certainty that you have an mde file.