I have had similar problems...
In my case one user locks the cdx file or memo file for an update on a large table...Via RLOCK().
The next user attempting to do a tableupdate() on this table gets..

'record not available please wait....'
or 'record locked by another user...'

I tracked the problem down.
Two problems.
1) The server program useed no buffering while the client program used buffering.
2)Changes the lock and write order

At any rate what I did was...

=SYS(3052,1,.T.) && Changes the lock and write order
=SYS(3052,2,.T.)

And check that buffering is the same in both application acccessing the same tables...

Not sure if its related but...