I forgot to mention that the way I fixed(?) the problem was by adding a new
module to the project, copying all of the code from the offending module to
the new module, removing the offending module and then renaming the new
module with the offending module's name. This worked.

I still would like to know why Option Explicit failed in the old module.

"cgr" wrote:

A module in my project allows undeclared variables to be created even though
Option Explicit is defined.

Any idea why?

The remaining modules (all defined with Option Explicit) in the project do
not allow undeclared variables to exit.