[]nosleep said:
hmmm, if I take the www out all users get this on submit:
The host you are trying to send the input from is not a valid host.
Please use your back button to return to the previous page. [/]
Use whatever one you use normally - that error you get is the referral check, which you can either turn off in your admin area.
You also should list both domains for the referral check:
Control Panel -> Primary Settings -> Advanced Options
In the box that says "Domains for HTTP Refer check" separate them with a | per the example.com domain shown there.