IF Statement in Vugen for HTTP/HTML

Hi ive created a script in HTTP/HTML and sometimes when i run it because we only have limited user ids it says the user is already logged in and opens a pop up asking if we would like to log the user off his current session? or if we would like to exit logon? ..

I need to write an IF statement so if this occurs the script will click yes log user off

Can anyone tell me how to do this please?