Database upgrades can fail for 2 reasons:

 1. The database cannot be found because it is in a non-standard location that 

    MediaMonkey could not find.

    To resolve this update MediaMonkey.ini with the path using DBName:

    http://www.mediamonkey.com/support/index.php?_m=knowledgebase&_a=viewarticle&kbarticleid=46

    Or if you're upgrading from MediaMonkey 2.x run MediaMonkey from the command line as follows:

    MediaMonkey.exe /OLDMM2DB [path to old database]

    For example:

    "C:\Program Files\MediaMonkey.exe" /OLDMM2DB d:\MediaDatabases\MediaMonkey2\MediaMonkey.mdb

    note: "" are required for paths containing a space

    This will cause MediaMonkey to detect and upgrade the old database when 

    it runs (note: if you're not prompted to upgrade the database, it is either 

    because the old database cannot be found OR because a MediaMonkey 3 

    database already exists (in which case you should delete it).

 2. A database failure has occurred during the upgrade process.  

    Sometimes this can be resolved by installing the previous version of MediaMonkey

    which was installed (http://www.mediamonkey.com/support/index.php?_m=downloads&_a=view&parentcategoryid=2&pcid=0&nav=0).

    After installation, open MediaMonkey and go to File > Maintain

    library. In the window that appears, check "Optimize database (complete)". After

    the process completes, reinstall the latest version. If this fails, your database may

    have become corrupt.

    For causes and solutions to such corruption, see: 

    Error: Database Image is Malformed:

    http://www.mediamonkey.com/support/index.php?_m=knowledgebase&_a=viewarticle&kbarticleid=78