I found a strange source of similar errors which may not apply in this case, but did drive me crazy for a week. The Encode module, rather than hard-coding VERSION, uses CVS tags for Revision with code to translate that tag into standard numbers. It is nice for developers, I am sure. Unfortunately, I checked some pm files from Encode into my CVS along with other code. The end result being that my CVS changed the revision tag, and thus the apparent version. When the version did not match the .so file, it broke. The only reason I discovered this was that I recompiled, checked the new pm files into CVS and the revision number in the error changed. Now, I am not sure how many other people check third party perl files into their CVS, but this is definitely one possible cause. And since I stumbled across this page while trying to figure out that very problem, I figured I should mention it in case someone else is having the same problem.