What hardware are you using? And are you using example code, which one?
The error you are getting indicates that the device handle you are attempting to use is not a valid resource on this system. Based on the front panel screen capture you provided it looks like you are attempting to use a device named "RFSG" on your system- is this the alias of the hardware you are attempting to use? Are you just attempting to run the niRFSG close VI by itself?
I recommend taking a look at the NI-RFSA and NI-RFSG shipping examples, and if you are having problems with a simple VI you created please attach the VI to your post- it's very difficult to troubleshoot when we have incomplete information.
I am using 2 MIMO's blocs, one with 4 NI 5663E (3 slaves and 1 master), and other with 4 NI 5673E (3 slaves and 1 Master also). I just found the solution, this morning, the problem was due to an obsolete vi, I just take a Labview 2012 version of some vi (like niRFSA initialize, and some others ) and the problem was solved !
Thank you for helping 😉