beaTunes does not start, shows JDBCException

After an unintendend shutdown, a power outage or an application crash, beaTunes may not start up properly anymore.
If beaTunes displays an error message mentioning a GenericJDBCException the internal database may have gotten corrupted.
The easiest way to recover from this problem, is to simply delete beaTunes' internal database. This does not harm iTunes or its database or your songs in any way.
To do so, you need to first shut down beaTunes. Then

• Windows Vista/Windows 7 Delete the folder C:\Users\<username>\AppData\Local\tagtraum industries\beaTunes\database
  
• Windows XP Delete the folder C:\Documents and Settings\<username>\Local Settings\Application Data\tagtraum industries\beaTunes\database
  
• OS X Delete the folder ~/Library/Application Support/beaTunes/Database
  (the ~ character denotes your home directory)

These paths are valid for beaTunes 2.1 or later.

Important

By deleting the internal beaTunes database, you lose all data that isn't stored in iTunes or the audio files themselves.
Usually that's color, key, decimal fractions of the BPM, language, PUIDs and tags.
To embed color, language etc. into the audio files themselves, check the corresponding option in beaTunes' general preferences.