I was having problems with SW Explorer. SW Explorer was having trouble finding all references for a file, sometimes not even finding a file that I could find manually.
I tried all kinds of things: monkeying w/ Windows indexer, writing API to replace search functions. Today I seem to have found the answer...
Under Windows (XP Professionall) Control Panel --> Add/ Remove Programs, select SW Explorer. There is a link named "Click here for support information", click it. Then, click the "Repair" button.
Took about 30 seconds, then all was well. Where-used and Pack-and-Go working as-advertised.