Found this on old Sage KB. Error 54 ""Unable to load error handler"" occurs when any error is generated before the error handling is established in the sequence of startup events. If possible, open the debug screen to find the program and line last executed to determine the cause. The system may be unable to write to a session file or some other file involved in the startup process.
Resolution 1: Permissions to the share folder are incorrectly set. Verify that permissions are adequate.
Resolution 2: Verify that file attributes are not set to 'Read-only'.
Resolution 3: A file may be locked. To resolve, restart the workstation and server, if necessary. There are additional suggestions, but check these first.