Unknown O-Tune Error - in MATUNE when removing monitors

Products

• Mainframe Application Tuner

Issue/Introduction

When trying to remove monitors from MATUNE received error: "Unknown O-Tune Error"

Pressing PF1 shows error description of:
Unknown O-Tune Error - Unknown Open/MAT failure. RC=12 RS=0; MSG1 = TN5134E
Invalid monitor data set length, pattern, or variable specified for profile
<profile>; MSG2 = 

Environment

Mainframe Application Tuner R12.0.  MATUNE

Resolution

Firstly, go to the Primary Option Menu, enter 0 for their Parameters. 
Check the value that is in "Monitor data set" in the "Monitor Data Set Options" section. 
A typical value is: 
Monitor data set ===> 'CAMAT.&USERID.&PROFILE.&SYSDATE.&SYSTIME'
Note that the dataset is comprised of nodes based on variable values.  
This is a good practice to prevent duplicate dataset errors as well.

Please ensure the dataset format is correct for the monitors.  

If the above has failed:
A cold start of the server will remove the pending invoked monitors. 
Stop the server normally and then issue /S SERVERNAME,START=COLD.