Internal Server error Saving settings with "$"

[GoodOmens]

I have a strange error in one of my forums where if I save any settings (or send any emails) with a $ in them I get an internal server error (From the Admin page). These are the template holders.

Posting messages to the forum works fine (Although haven't tried adding the dollar sign).

I would normally think it's a mod security error, however I have another forum on the same server with very similar settings and I get no error.

The htaccess files in the two settings are almost identical and I've tried re-uploading the files on the "bad" server.

I also have PHP safe mode enabled on the two.

I've tried adding:

PHP Code:

<IfModule mod_env.c>
SetEnv MODSEC_ENABLE Off
PassEnv MODSEC_ENABLE
</IfModule>

#vbulletin
php_flag magic_quotes_gpc off 


To no avail. I've also tried disabling plugins via the config file and still get the same error. I'm running php 5 and Apache 2.x

Like I said this works on one install but not the other install on the same server.