What would cause me to not be able to click on the tab of a page in a page frame?

I've got 4 tabs on a cBizObjMaintenanceForm, and I can click amongst tabs 1-3 with no problem, but once I click on tab 4, I can only click back to tab 1 (the List), and can't click onto tabs 2 or 3 until I click back to tab 1.

Tab 1 is the List, tab 2 is the Properties (I've renamed it, but that's what it was) Tabs 3 & 4 I've added. 3 is currently blank except for OK and Cancel buttons. Tab 4 has a bizobj on it where I've checked auto primary bizobj.

Thanks,

June