If they are "minor" errors that don't impact on the bot crawling activity, they should not have any impact.
Have a look at a google official response :
http://www.youtube.com/watch?v=moDRehiE2ME
I always prefer however to have a totally "clean" website...
ps
here you can find a transcript of the video :
http://www.ishoppingcartsoftware.com/Video/12913/can-coding-errors-affect-how-a-page-is-indexed
(I've found only this link...)
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