When developing a website using 4D as a backend, 500 internal server errors may be encountered when testing client requests to the server. Usually, this means there was an error in the backend code. To troubleshoot this, ON ERR CALL handlers can be installed to catch the errors when they occur. Alternatively, if the method in which the code is executing is known, put a TRACE or breakpoint at the beginning of the method. Then, when the debug window appears, select the play button to let the code run and hit the point of failure, at which time the error will be shown.