It looks like the Toodledo sync is a Pro feature on Task Unifier. You probably need to upgrade first before entering your Toodledo credentials. If you did upgrade and the sync still doesn't work, you should contact Task Unifier's customer support so they can fix the problem.
I did get the same message from both Task Angel and Task Unifier that the User is being blocked. I put a ticket in but got a standard answer that it was third party software. I don't think this is the answer for 2 programs to give the same error message. I wonder if it has something to do with change from Toodledo Pro to Toodledo Gold.