The Machine Tool Navigator tab is missing from the Resource Bar
Solution
Close NX
Remove the contents of the folder C:\Users\<username>\AppData\Local\Siemens\NX1953 (do not delete the folder itself).
Restart NX
The Machine Tool Navigator tab should now appear in the Resource Bar.
Notes and References
Hardware/Software Configuration
Platform: INTL64
OS: windows
OS Version: 10_1507
Product: NX
Application: CAM
Version: V1961
Function: USER_INTERFACE
Ref: 001-9994232