DEAD LOCK Problem

Try to use google on deadlocks, blocks or locks.

If a user changes a record a lock occurs. If another users wants to modify the same record a block will appear. If user A locks record X and wants to lock record Y and user B locks record Y and wants to lock record X a deadlock will occur.

The database driver will decide which user is deadlocked based on costs.

To solve deadlocks try to minimise posting routine durations.

Good luck.