Fatal error for registering on fronthend

New users cannot register themselves on the registering form. After filling the form and sending, Page becomes blue with a message

Fatal Error.
An unrecoverable error has occurred and has been logged. 
Contact the site administrator with the following information:

Exception at time 2022-09-09T20:08:33+00:00

When I look up the access logs on my hosting server, I get the errors similiar the one below:

POST /action/register HTTP/1.1
Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/ Safari/537.36
United States of America

How can I overcome this problem? I need your urgent help.