Have you reinstalled and patched yet? You've got some corrupt files. You could try the WoW repair tool, but my experience showed that it wouldn't work, no matter how far back it rolled the patches.
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People don't like to be meddled with. We tell them what to do, what to think, don't run, don't walk. We're in their homes and in their heads and we haven't the right. We're meddlesome. ~River Tam
Sedao