moshu, I hear you on the human errors but to be honest I am pretty sure a plugin did this.
Why? Because I have deleted a plugin in the past(had a backup so repaired asap) that when I decided to remove it, this error appeared. It had been a while ago so I forgot and cleared out some deadwood plugins today.
Also the error occurred literally right after I deleted 3 plugins. Now it is possible I deleted something else but anything to do with my header if deleted is more likely to cause a significant problem other than a cosmetic one like this (I would think-am I wrong?).
Also I could get on board because of the plugin problem before with a corrupt file but am not sure what I can do about finding such a file.
Hmmmm, by the way I went into admin-header.php and deleted the < there as well and now the dashboard is fixed. So I can hobble along like this but I am worried this could cause problems in the future.
Should I just wait until 2.0.4 comes out in a few days and when I upgrade maybe the corrupt file will be overwritten.
I don't know, just babbling. STRESS!! :)