211885312 Up Port. Ff to 4.0, Lost Library
XP operating system. 'Two copies of Firefox (Ff). First, C:; second, external drive (Passport). Portable (Pt) Ff on the Passport. Upgraded the Port. Ff 3.6 to 4.0, library gone. Read Zotero "Where did my items go?" 'Found two locations with .sqlite. Assumption: one .sqlite path is for laptop Ff; other for the Passport, Port. Ff, copy. Add symptom: At Launch Port. Ff, indicates that it is 3.6, actual version of Port. Ff is 4.0.
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If you make copies of all your zotero.sqlite files you can't really break anything - so you can essentially try which one works: find the respective data directories of your Zotero as described in the documentation and then place the sqlite there.
http://www.zotero.org/support/forum_guidelines#don_t_create_redundant_threads