I am trying to add custom field to a bug in TFS.
I opened the Bug Work Item Type but i have to enter the RefName as show in the image below.
Does any body know how can create Custom RefName

I tried to do as Ewald Hofman said, i got the below error
Sign Up to our social questions and Answers Engine to ask questions, answer people’s questions, and connect with other people.
Login to our social questions & Answers Engine to ask questions answer people’s questions & connect with other people.
Lost your password? Please enter your email address. You will receive a link and will create a new password via email.
Please briefly explain why you feel this question should be reported.
Please briefly explain why you feel this answer should be reported.
Please briefly explain why you feel this user should be reported.
Just enter a name. It is used as the identifier for the column in the rest of the work item and in the warehouse.
A possible format is YourCompanyName.Category.FieldName