FAQ.How do I enable/disable a single tab in a tabpanel?
Feedback.

Answer: Try this code:
Example:

dim err as integer
declare function SetTabEnabled lib "AppearanceLib" (tabcontrol as Integer, tabindex as short, enabled as boolean) as Short

err = SetTabEnabled(tabpanel1.Handle, 0, true)

Notes: Use Carbon for MachO and CarbonLib for Mac Carbon and AppearanceLib for Mac OS Classic as library.