Ask if they have mod_security turned on with the server you’re hosting on. If they’re any kind of good host then they most definitely will have this turned on.
Tell them the problems you’re having and if they think it might be related to that as it might be thinking that the from is part of a database query and thus not allowing the post to go through. On that note I’m just wondering what word(s) you have surrounding the from?
Anyway they will let you know if they think that is the problem. They will probably ask you for the paragraph of text that isn’t going through and then they will test it their end.
Once they find out if it is indeed that which is causing the problem then they should be able to place an exception on your site to allow that to go through. This is a lot of the time done by a line or two in a .htaccess file in the root of your website.
Just out of interest in the meantime though what was the paragraph of text that had that word in it? Can you post it here.
Also if you try posting the entry without that word in does the entry post? That will help to narrow things down too.
Hope that helps a bit.
Best wishes,
Mark