Why can't I log-in using a forwarded website?
 

Why can't I log-in using a forwarded website?
I have 4 website domains. Lets say my main website domain is called www.MainWebSite.com...... The remaining three websites www.Forwarded1.com* www.Forwarded2.com* and www.Forwarded3.com are forwarded to the main website (www.MainWebSite.com) on GoDaddy.

So you can log in from the www.MainWebSite.com* however* when you try to log in from any of the other websites* it loads and looks like everything works* but then it bombs out* and it's as if you never logged in at all.

So why can you log in to the Main Website* but any forwarded one will not log in? Again* the forward works because you can see the site* you just can't log in from those websites.

How can you correct this?