Oh I just hate those emails that help in no way what so ever. Firstly I doesn't even look like they even looked at it to see if it was causing the problem. They say they cant do anything because the settings are preset by the system administrator. Who is probably a contract worker who pays by the hour and isn't there on site and they can't be bother to send him in.
They are so blantly wanting you to sign up for 3rd party script support. I have no idea what good what will do since it may not be the scripts fault at all. Unless you have edited the php files at all? But I doubt that a program that has had many years of work done to it and where over thousands of people use it aroud the world will be able to be fixed by a hosting company.
I can see that at this stage they are not wanting to even touch on the subject that they might of missconfigured their server.

I suppose the only thing you can do is search around to look for other explanations, although there are few. You could also try a fresh intstallation in a different folder and making a different database and seeing if the problem is the same. That way you know it's not because of some setting that you might have changed.

You could also try and have a look round to see if other people are having the same problem and are on the same host as you. Proving that you are not just a one of case.

You could also try and make a simple script that use a form that will use the post method to send the data to the server. Where if you get the same error when posting data in the form and there are no errors in your code you could show them that.

Hopefully you are able to grab their attention somehow or find another possibility for the error.

Otherwise you could always switch hosts :P

Hope that helped or gave you some ideas. If anyone else wants to add any other Ideas dont let me stop you.