I forgot to answer the below question:

The strange thing is, when I comment out the entire code, I still get
the error.

I beleive this is because the normal function of double-clicking a cell is
to enter Edit Mode. This is not allowed for locked cells when the sheet is
protected. Therefore, this should cause an error message whether you had
created code or not. However, I wouldn't expect you would get the same
message. Rather, somthing to the effect that you can't change protected
cells. I get:

"The cell or chart you are trying to change is protected and therefore
read-only..."

Regards,
Greg