There are so many situations with Outlook that can cause this exception that it is almost impossible to suggest a guaranteed solution. The links from Abhinav are a good starting point but if they do not lead you to a solution I would suggest that you use use the error message as a search phrase and search the web.
If you do, you should get over 32,000,000 hits. From there it should only take you the rest of your life to go through them.
Seriously it is just a matter of looking through them trying to identify one that matches your situation.