I've run into a bizarre problem where IDEA tells me that it cannot resolve symbol for classes within the same package as the class open in the editor. And, if I use Alt-Enter to add an import line, the import line shows up as greyed-out for 'unused import statement' (but the 'cannot resolve symbol' flag goes away). Similarly, there are a number of classes being flagged with cannot resolve symbol while there's a greyed-out import line that contains a wild-card import that includes those flagged classes.
This is in IDEA 9.0.4 and only just started happening.
Invalidating the caches did not fix the problem
Deleteing the cache files in the filesystem did not fix the problem
Deleting the module and rebuilding it did not fix the problem
Any other ideas?