No "Grant Access" link
I've sent an invitation to my Gmail account to access my AdWords, and clicked to accept the invitation and sign in to Google. However when I go back to the primary AdWords account, there is no "Grant Access" link as the Help FAQ describes. The Gmail invitation (and it's previous invitation) still show in Pending Invitations, with no way to grant access.
Re: No "Grant Access" link
Are you sure your gmail account has access to your account? There's a little trick to doing this properly. When you click on the link in the email, on the next page you need to check the box that says "I already have an account". Otherwise, a new account is created.
Log into your AdWords account as you normally do. Take down the account number. Now login into AdWords with your gmail account. Is the account number the same? My guess is that it is not.
You will need to remove the gmail address from the new account before you can try again. Or use a different email address.
Best of Luck!