[Logician]

Blanks screen usually means there is a PHP error in your code and server is repressing it. If you run the script (get blank page again) and then go check your error log file, you should be able to see the error message which should give you a hint to fix the problem to your external script.

As you know in iframe method your external script does not deal with other scripts running outside iframe so I don't think there is a confliction with webtemplates, it sounds like a problem on your script end.