This means that GEM can't locate the file. If you use an absolute path (with / for instance), then GEM will look there. Otherwise, GEM will look in the directory of where the patch is. Then pd/GEM will search the paths you specified at pd-startup with the -path flag.
Check the following:
- Does the file exist?
- Did you make a typo in the filename?
- Is the file in the search-path ?