Hi,
I've just installed multisites and followed the tutorial.
Initially, when I clicked on the link to go to the slave site installation instructions, there was nothing there, so I assumed I had to install everything prior.
So I uploaded the Joomla package and then installed and am getting the 500 internal server error..
I hope someone can help.
Kind Regards,

I have also found that it has stopped my webmail component (provided by Open Source Excellence) from working...
I need urgent help with this please.

It has also killed my Comet Chat installation..

JMS does not touch anything concerning the webmail or extensions like comet chat.

The Error 500 mean Internal Server Error.
In general, you have an "error log" file in your server that give the reason of the error.

Amoung the potential reason you have:
- Files and folders permission;
- Fatal PHP error to read or access a file;
- .htaccess syntax error, ....

So check your "error log" file to get more info on the reason of the "internal server error".