Just recently upgraded to Eclipse 3.5.1 RC1 and started getting this error in the console when trying to search for classes:

I tried cleaning, closing projects and even downgrading to Eclipse 3.5. No luck. Found this post on stackoverflow.com with the solution:
- Close Eclipse
- Open/cd into workspace folder
- Delete .metadata/.plugins/org.eclipse.jdt.core/*.index
- Delete .metadata/.plugins/org.eclipse.jdt.core/savedIndexNames.txt
- Start Eclipse again
Followed those instructions and eclipse is happy to search for classes again.
