I think I dun goofed.

[The Guy]

So, I tried first upgrading v4 Beta 3 to Beta 4 and the results were that I could not sign into the site, but I could sign into the admin panel. If I signed in it would just refresh and still stay at Guest. Then, I decided, "well, oh well, after all it is a beta" and deleted the database and recreated one, then a whole fresh new install. Same thing occurred. Could only successfully sign in to ACP, but not Forums, Downloads, or anywhere, it would just refresh and still as a guest. 

Notice I had no issues with Beta 3, only severe problems with Beta 4

[Joriz]

Can you provide some more information? Can you see with the debugger in your browser what is actually happening when you try to login?

Please notice you can also report bugs in the bug tracker.