I googled the issue and it seems to be a redirect issue with vbulletin. The thread I found is here:
This problem occurs when you don't redirect hi5arena.com to www.hi5arena.com.
Your actual site is located at www.hi5arena.com but there are people who will not use the www. and simply enter the domain. When they enter their login details, it looks as if they are loggin in but they are redirected to the wrong domain so it kicks them back out again.
Do a 301 redirect from hi5arena.com to www.hi5arena.com.
AdminCP > vBulletin Options > General Options > Post Referrer Whitelist
Add hi5arena.com to the box and save.
So I tried logging in to http://www.nvnews.net/vbulletin
instead of http://nvnews.net/vbulletin
and it worked. Try it and let me know if it works for all of you.
If so then a simple redirect from MikeC will fix it for good
If not... then it's back to the drawing board...