Buttons are pretty basic, they have a handler to point them to a function. either there is no handler, or the function can't be found. [edit] What I wrote above is pretty bad in hindsight. Changing to masterpages alters the ID of the button, and prefixes a $CT100 to the ID name. I'm trying to think of how this would affect your content pages. Can't think of anything. All I can think of is that you left your click functions on the master page code behind, and did not move them to your content page code behind.