Just to close this out in case anyone else has this problem and stumbles across this thread. There was a typo in one of the WeBWorK source files:
The file ListingDB.pm on line 366 had DBsection where it should have had dbsection. I edited that line, restarted apache, and all was well. I believe the source on github has been patched too, so this error is unlikely to affect others.
Hal