I was having the exact same problem as above.
Prior to the "symptoms", I installed the application in a newly created folder on the C drive (Not the Program Files default installation directory).
I then changed the name of the folder directory where the executable was installed to enable a third-party script to launch the NetBeans executable as the script required no spaces in the path. In any case, in attempting to uninstall the application again, I got the above error.
I tried running the command as outlined above (namely) running the command prompt with the following:
C:\Netbeans\NetBeans 8.0.2>uninstall.exe --userdir C:\Users\mark.burl.nbi
it launched the uninstall but the same error popped up.
I then undertook the following and the problem was solved for me:
- I manually deleted the NetBeans executable folder.
- I then reinstalled NetBeans to the default Program Files location.
- I then uninstalled NetBeans again no problem.