Forms Authentication folder permissions

I have an interesting problem on an application that I didn't create but am now tasked with supporting.  I'm hoping someone who has some experience with Forms Authentication can help me out.  I have this code in my web.config file which hasn't changed, the IIS website settings haven't changed.  The only thing that was changed is that the permissions on the folder got blown away.  Other sites on the server work fine, but they don't use Forms Authentication.  We've reset the permissions to:

Permissions

CREATOR OWNER - Full control
Authenticated Users - R/W/M 
SYSTEM - Full control
Administrators (server\administrators) -Full Control
Users (server\administrators) - R/W/M
IIS_IUSRS - R/W/M

And the web config shows

Web Config

<authentication mode="Forms"><forms loginUrl="~/Login.aspx" timeout="2880" defaultUrl="default.aspx" /></authentication><identity impersonate="true"/><authorization><allow users="?" /></authorization>

I've tried every combination of permission settings that I can think of.  Can somebody please help me figure this out or point me to a clear (Sorry Microsoft) resource to understand Form Authentication better?  I'm desperate.  Our site is down.

Also, if this makes any difference, this site uses two different web services.  However the permissions on those folder haven't changed and they're used by other sites on the same server that are working.