This happens when we enter a CONNECT Account credentials on the APM Server Manager web page and click “Log on as Bentley CONNECT user”. We get an error saying "The custom error module does not recognize this error as shown below :-
In order to use CONNECT Account credentials in the APM Server Manager web page, we need to log in by typing the CONNECT Account credentials into the textboxes for 'Log on as Windows User' in the web page rather than going through CONNECT.
NOTE:- This issue has been fixed in 7.12.
VSTS - 47152 SR - 7000891749