Have you tried:
– deactivating all plugins to see if this resolves the problem? If this works, re-activate the plugins one by one until you find the problematic plugin(s).
– switching to the default theme to rule out any theme-specific problems?
– resetting the plugins folder by FTP or phpMyAdmin? Sometimes, an apparently inactive plugin can still cause problems.
– re-uploading the wp-admin and wp-includes folders from a fresh download of WordPress?
– increasing your available memory?
Thank you I also found another post that referred to a similar problem and mentioned plugin POLLIN – and hey that is the one I had installed. I have de-activated and deleted it AND hey presto I now have access to widgets again.
Thank you.