Disclaimer: Turn it on only when asked by support person to reproduce your problem and help us fix it. It can cause serious performance issues.
To turn on error logging in AD FastReporter you need to add "/log" argument when launching AD FastReporter.
After the problem is reproduced, close the program and find the error log (ADFastReporter.log) in AppData folder that usually is C:\Users\USERNAME\AppData\Roaming\AlbusBit\ADFastReporter.
Do not forget to remove "/log" argument from your shortcut.