Based on the description of the problem, you most likely have the Silver Edition (the original game and the expansion with the dwarves on one disc with patches 1.5 and 2.1).
Due to our "talented" localizers, patch 1.6 cannot be installed on 1.5; no prayers or magic will help here – this is an official bug. :)
The only way to install 1.6 on the Silver Edition is with this cumulative patch.
P.S.: It would be good to leave this topic open, as few people know about the bug with the Silver Edition.