Some modded commands incorrectly implement a certain piece of code. This piece of code is used for sorting the list of commands alphabetically in the /help command. This incorrect code actually causes the /help command to break with an error that is vague and confusing.
HelpFixer changes the /help command to go around the offending code and sort the commands by a method that will work. HelpFixer also logs offending commands to the server log, allowing you to figure out who was causing the problem.
HelpFixer is a server-side only mod! This means HelpFixer should be installed wherever the "server" is. In SSP that is your client, but in SMP that is on the actual server.