@WPyogi: In the absence of a new thread I'm going to post here.
@Wizastudios: Mine was plugin related. Bizarrely, the first thing I did was to rename my plugins folder in order to deactivate all of my plugins at the same time but the problem persisted, which threw me off the scent for a while - so I'd recommend this as a first port of call:
Try deactivating your plugins one by one, trying to login via the editor account after each deactivation. Hopefully, it will be plugin related and once you turn off the offending plugin, the problem will resolve. You can then make a call on its functionality - maybe switching it out for something similar that doesn't cause the conflict. Mine was an 'under construction' plugin. I had switched it off via a switch in the plugin rather than deactivating it properly. Once deactivated, the problem resolved.
Good luck with your troubleshooting - I hope this helps.