A while ago we received some unexplainable errors on the servers desktop. A popup window would appear with the Title "Error" and three buttons "Abort, Retry and Ignore". That was all the info we got. When the popup was shown, IIS stopped responding all together until one of the buttons was clicked.
We had to call in the assistance of Microsoft and after numerous troubleshooting sessions we tracked down the issue to the Search component of SharePoint.
A user has uploaded a picture of himself to a picture library. He wanted to use that picture as his profile picture, so he copied the URL of the page (not of the picture) and managed to somehow paste this into the ProfilePicture URL field.
Unfortunately the picture library had spaces in the URL and when opening a picture, SharePoint always places the location where the user came from in the URL. Because the library contains spaces, were these URL double encoded:
Percentage sign: %25
Double encoded space: %2520
This caused the user to paste a double encoded URL into his ProfilePicture field. As it turns out, SharePoint throws an assertion error when it is requested to return this value, for example when searching for that specific person.
After discovering the issue, the Microsoft engineers checked internally and found out that coincidentally the issue was fixed in MOSS Service Pack 2. They redesigned the assertion handling in this service pack, fixing the issue.
Before we implemented Service Pack 2 on our environment, we changed the value is the users profile to a correct value and ran another crawl. Fortunately we never saw the issue ever again.