If you don't logged in, viewing the board as guest.
Go to calendar -> click the events -> it shows a list of member who have birthday -> click the "member name" -> it display this:
"FATAL_NOT_LOGGED
Please use your back button to return to the previous page."
I think instead of FATAL_NOT_LOGGED -> a clear error message is needed.
You can see this error by click this:
https://www.ubbcentral.com/forums/ubbthreads.php?ubb=showprofile&User=2362