Bear in mind some functions in the program are context sensitive, and will not become active until you meet the conditions for them to appear. For instance, if you don’t have a 3d mesh in edit mode, many functions related to mesh editing will not appear. Likewise, if you have custom brushes installed on an interface, these will not show up unless the brush in question has been loaded into ZBrush.
If this is a UI that has been created in a previous (year) version, it should probably be discarded and re-created in the current version. UIs created in older versions may reference functions or content that has changed, leading to glitches and even possible program instability.
If you don’t believe any of the above applies to your issue, you should head over to Pixologic Support, and start a conversation there.