The CopyObjects method only has two args, so the problem has to be one of them. You might not get an error, but blkDef could still be null. That's why I asked what is its status. Set a breakpoint on the CopyObjects line and see if blkdef is set or is null. Also, you might not get an error if you have used On Error Resume Next somewhere in your sub.
You were so right, I didn't reset the error handler in that module. Sigh.
Added the error handler back into that module (at the appropriate location) and ended up with the same error.
Based on the variable watch, both of the arguments have values.
Pulling my hair on this one.
I even purchased an Autocad VBA book by Lee Ambrosius (AutoCAD Platform Customization) that was more up to date than my other ACAD VBA book.
Based on his book my code should work.