who's your host?
I'd be looking for a new host after that response if it where me.
create a new blank page wit the following code:
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
<meta http-equiv="Content-Type" content="text/html; charset=UTF-8" />
this should produce the same error and convince the host that it is not a scripting error.
all this code is doing is turning error reporting on, then calling the session_start(); command. This is not complex code and should be able to run in any hosting environment that supports session management.
The host expecting you to change the php.ini is bogus, this is something they should be able to fix for you.
to be honest, I have come across this issue a number of times, and this is the first time that the host has refused to fix it . unfortunately though, it is an issue they will need to address if it is to be addressed at all.
the problem is the session.save_path setting in the php.ini file.
it looks like it is currently set to "D:\Webs\bigmo8\data\php\session\" but that location cannot be found.
I cannot say what it should be set to, but the host should be able to.