Some hosts will disable/remove the scripting component for security reasons. I had a similar problem with our hosting company. I'd been using the FSO fine but after they'd moved to a new server they'd disabled the FSO part of the scripting component. It wasn't a huge deal for me as I was able to convert the files I was using to XML format and use the MSXML parser instead.
In your IIs managment Console, find your web then right click the diesired directory, propertise and permissions (off the top of my head) you should then be able to see what users have what permission. the IUser should be there but might not be, if it is change the permissions to write. if the IUser is not there click "Add User" and then find the IUser account and give it Write permission.
The IUser is a built in account installed by IIs, any users that are loggin in anonymously to a webpage get logged in to that account