I tried to add this to my Zen Cart, thought I had done all correctly but am getting the error codes below:

Warning URL was not shortened for Twitter: http://www.comedyshirts.co.uk was used instead. Reason: INVALID_LOGIN
Error Twitter could not be updated: 401 Unauthorized: Read-only application cannot POST
To paste the code into twitter yourself use:
New product available: 'Your design' mug! Check it out now at http://www.comedyshirts.co.uk

Help would be much appreciated.

Thanks
Tony