It's should be either concurrent update using optimistic locking or the row was removed.
In practical way.
This exception can be caused by the triggers on the table, which you want to update.
I had that problem on: jboss/tomcat + mssqlServer2K.
It helped when I put 'SET NOCOUNT ON' clause in trigger.
CREATE TRIGGER [ON_INSERT_SOMETHING] ON dbo.kurs FOR INSERT, UPDATE AS SET NOCOUNT ON ....