I've tried to setup a Contributor but when I go to validate I get an error that reads, "The Account you validated in Twitter does not correspond to the Account that you selected on Salesforce"

Here's what I've entered in my Contribitor setup fields:
Contributor: SalesForce username
Username: SalesForce username
Twitter Account: Twitter account username
User: SalesForce username

When I click on VALIDATE, it takes me to the Twitter authorization page where I enter my Twitter credentials (which I've triple checked), but then I get the above error message.

Any ideas?

Thanks,