“Diagnose” Button is Grayed Out

I am a fairly new user.  I have only 2 accounts & their setup seemed to be rather straightforward – with One Exception::
     On ONE of the 2 accounts, the “Diagnose” Button (In Tools/Accounts/Diagnostics) is Grayed Out (It Does Nothing), and I would really like to test it to check if everything is working fine.

Could you Please help me to get “Diagnose” UNgray?  I would really appreciate that!!

(I am using the Latest Version of eM Client.)

Thank you very much for your Help!