This is a known defect in PM 2.6 (build 18.104.22.168)
The fix for this defect is to either apply the PM 2.6.0 December Update Kit (build 2.6.071) or upgrade to a newer version of PM.
To find out which CAPC build you are running, go to your CAPC UI > Help > About. The "About CA Performance Center" window that is displayed will show the exact CAPC version you are running.
Note: Technical support for PM 2.6 and PM 2.7 will be discontinued effective May 1, 2018. See Additional Information for details.
It is always strongly recommended that customers be on the newest version of PM. Newer versions have improvements and fixes for defects found in older versions.