I have a bizarre thing just happened in NetBeans - the red error markers on the LHS of the editor window have all vanished. There are still errors - the files are flagged as having errors, and the errors are correctly diagnosed when I do a clean/rebuild, but no error markers in the edit window and therefore no suggestions or corrections available. Other markers such as those that show overridden methods are still present. Similarly, all the little colored bars down the RHS are present, execpt those related to compile errors. I've restarted and rebooted. It's not just one file or project, it's general across NetBeans.
If anyone has any ideas or suggestions I'd be very grateful

Strange indeed; have you tried deleting the Netbeans cache directory at $userdir\.netbeans\[version]\var\cache\ or something along those lines?

OK, just tried that (it's in appdata btw), but no difference after cache re-built.

Update: Same project displays correctly in Netbeans 7.3.1, so maybe this is a recently-introduced bug in the 7.4 development version that I was using?