Recently I keep receiving those "Mutex.lock: error code 0" error messages as a Sys_error ( using system threads under Win32 ) The mutex protects a list, both inside an object, together with a thread iterating over this list. There is a method which allows other threads to add elements to the list, locking the mutex before accessing the list. Nothing special at all. The error seems so terribly stupid to me that I have no clue where to start looking for a workaround. If you could provide me with any information about the reason / documentation or where to find it, I would be greatly thankful. Thanks Sebastian -- 5 GB Mailbox, 50 FreeSMS http://www.gmx.net/de/go/promail +++ GMX - die erste Adresse für Mail, Message, More +++