'clear defaults' button not enabled

[cfdenice]

Hi,

My stock email app is the default app and runs when I tap on it's icon. I'm trying to change which email app runs (from stock app to some other email app) when I tap on the email icon. The problem I have is that I can't 'clear defaults' on my stock email app because the 'clear defaults' button is not enabled. How do I get around this?