When our support staff are creating a new request record they type the requester name into the appropriate field. Most of the time it auto-completes the name to match an existing requester account (imported from AD) and everything is fine. 

However, occasionally they mis-spell the requester's name and just hit the return key. When they come to save the request record they are getting a pop up window which says "Requester Name does not exist. Do you wish to add new requester as part of submitting a new request". Obviously I would like them to answer no at this point and go back and correct the requester name. However sometimes (probably without really reading the message) they just hit the return key which is equivalent to clicking OK. The result is that a new, unwanted, requester account is created. 

Is there any way to prevent this behaviour? I would prefer it if they weren't offered the option to create a new requester. I tried setting " Allow dynamic user addition when the user is not imported in the application?" to No, but this hasn't had any effect. 

Thanks,

Roy