Already locked error

I have a user who entering orders and is somehow locked by other users who doing invoice. It not allways the same two users or the same modules it happens alseat once a day. the current workaround is the first user has to finish what they doing then the second users then can go back in and work away. The environmet is Navision attain 3.10a client , on WIndows XP pro client athuticiating Novell NDS and the Navision is on the WIndows 2000 server as a standalone. The all long in as database logins, and we using native Navision database not MS SQL I try to lookup this questions through the search and no real luck. Please if any one has answer to please help

It seems to me the mirror of the problem I have faced a few times. there is no pattern of locking and one-two times the only way out has been to restart the user who is shown to be responsible for locking. This locking also forms a chain a few times and some time is spent coming out of all user locks for the transaction to take place. Any suggestions are welcome.

Are you using Manufacturing? This problem is more seen in Manufacturing.