This is due to an XML downloaded during the game. The source should prohibit this, but at the moment it doesn't.
The solution is first to make a command line fetch:
./mattricks.py fetch
or
mattricks.exe fetch
depending on your OS (Linux above/Win below).
Find the XML:s with the text "NOT AVAILABLE" in them and delete them.
grep -H "NOT AVAILABLE" all_players*.xml
works for Linux/Unix.
Delete the database and import all xml:s with
mattricks.py import *.xml
or
mattricks.exe import *.xml
A good idea may be to make a backup of your old database before deleting it.
This is probably the major bug prohibiting a final version 0.7.
/Oscar