Gormets,
I had the same problem as you.
Before re-installing the game, go to http://www.blizzard.com/support/wow/?id=aww01698p and download the repair utility.
This utility will scan your patch.mpq file and will detect any corruption or errors that need to be fixed. Once it is complete it will roll back you game client to an earlier version.
When mine finished it said that it found some severe errors and it reset my game client to the original version, so I still had to download a new patch but at least I didnt have to re-install.
If you have saved the patches in a separate folder, then you can apply them one by one. If not, you can download the Full 2.0 patch from the blizzard downloader or from other mirror sites. I use the premium area in this site for downloads however the full patch had to be downloaded via the Blizzard downloader or another site like File Planet.
Hope this helps
Edit: I just found this on the blizzard site.
Note: With the release of 1.8.0 the repair utility (repair.exe) can now be found in the main World of Warcraft game directory on your hard drive.
I downloaded the utility before running it. The version that I downloaded seems to be more current. It was version 1.5 whereas the one in the aforementioned directory was 1.4 I believe.
Edit2: I had posted about this before but I guess the title wouldnt have help. in any case I'm including a link to the post so you can verify if it is the same error I got.
http://wow.allakhazam.com/forum.html?forum=21&mid=1165369162142664116#116541588056645780
Edited, Dec 7th 2006 4:22pm by Dartanicus
Edited, Dec 7th 2006 4:27pm by Dartanicus