Thanks for posting a bug report, but the bad news is that I don't think this is a bug with Greymatter Rather this sounds like an issue with your web host.
I just tried testing and it seems to work fine with using the word 'from' in an entry. An error within Greymatter won't usually show up as 500, rather as another error. This is definitely something you should mention to your webhost, particularly if you are paying for the hosting service.
Caveat, I don't have the gm_rss.cgi running, but I can't imagine that it would impact gm in this way. If other people are seeing this issue, they should post.
Coldstone, Thanks. I was begininng to become an expert at 1,001 ways to say from without saying from. I gotta tell you, it is more difficult than it would at first seem.
First, I will double check all I have done to see if I could have caused this problem somehow. (I can't imagine what it would be, but stranger things have happened.) If doing that does not resolve the issue I will check with my host.
If I remember correctly, when I installed the RSS deal I had to install some additional perl stuff. Maybe the source of this issue is in there. Regardless of the outcome I will post it here so that it may benefit others.