I saw these in the doc:
Boolean that is TRUE if an NvFBC object can be created from the calling process, FALSE otherwise. This field may read back as FALSE for one of the following reasons:
? The calling process is running with insufficient privileges (login screen / session 0, for example). See section Error! eference source not found… ?
A different application is running in full screen mode on any head.
But,many games will change the desktop resolution at the begining,there will be a heap leak if you do not release nvfbc object and recreate it.