Hello,
 
The program crashes if launched with a counter on a process that doesn't exist.
Or if a counter disappears
 
QPerfMon.exe ".\Process\%% Processor Time\SomeProgramNotCurrentlyRunning"
 
or
 
QPerfMon.exe ".\Process\%% Processor Time\SomeProgramCurrentlyRunning"
-> close the monitored program
-> crash
 
It would be better to display the counters that are actually available and add a comment like "not available" on the counter.
Or just unchecking the line into the list view, so it could be enabled later.
Anything but a crash :)