Automate Your Business Process - Assignment Rules

Hello

I can't seem to add "Sean Forbes" from the picklist:

Could not find the billing support case for 'Sean Forbes' and 'Edge Communications' with the specified settings.

He exists within Edge Communications but I can't find him on the picklist! I can't re-add him as it's then a duplicate - and it doesn't work anyway.

Please can anyone help - it's my last step in this challenge! 

Thank you

Demy