I get this exception a lot in the 4.0 beta.  The 
class that is not found is always an inner 
class.  Several different inner classes trigger 
this exception, although other inner classes do 
not.  The exception happens when I open the 
relevant file, or when I search for a term 
included in that file.  Sometimes while editing a 
file I get several such exceptions for the file 
all in a row.  My project was created from 
existing source+build file and the source is JDK 
1.3.