Found the answer:

Commands that Automatically Lock Records and Tables
DELETE of more than one record Entire table

Thank you.

Alex
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I was surprised by this behavior:

A table has buffering = 5.

In session one, one record is locked while editing (to prevent another user from editing same).

In session two, user deletes a different record with DELETE FOR cField = lcValue. Pointer goes to EOF(). At that moment I issue TABLEUPDATE(.T.,.T.) but it returns .F. indicating failure. The problem does not ocurr if session one did not have lock in its record.

The problem also doesn't occur if I say:
LOCATE FOR cField = lcValue && Actually there was only one record in this case
DELETE
TABLEUPDATE(0,.T.)

Question is why did the tableupdate fail?

TIA,

Alex