WWW random freezes

Our standalone game uses the WWW class to access a php script (for database access). In beta tests it all worked great, but now the game is released and played by a few thousand people, we get flooded by complains of crashes/freezes that seem to be rather random but are always on moments where the database is accessed. Some people say they always get crashes, others have it only rarely, and often people have many crashes one day and none the next. Of course, none of us here can reproduce any crash.

An example of a log sent by a player:

 --2--
 Call set_items
 DB set_items  took 0.64 s
 Crash!!!
 SymInit: Symbol-SearchPath: ...
 --3--

Here are the relevant scripts that produced this output

Any help is appreciated!