[asp.net] Error to use a section registered as allowDefinition='MachineToApplication' beyond application level

It is an error to use a section registered as allowDefinition='MachineToApplication' beyond application level.

The top line in all of my aspx pages in my /portal/ directory has this error message, and I know it's a common one. I have googled this error message to no end, and I see a lot of posts telling me to configure the /portal/ folder as an application in IIS (which I have), and more posts telling me I have nested web.configs (but none of the postings offer guidance toward a solution).

My setup is that I have a web.config in my root directory, and then I'm trying to make a company portal, in the /portal/directory. The /portal/ directory has its own (necessary) web.config.

My web.config line 50 is like this:

    <customErrors mode="Off" defaultRedirect="customerrorpage.aspx"/>
    <anonymousIdentification enabled="true"/>
    <authentication mode="Forms"/>
    <membership defaultProvider="MyProvider">

So I have domain.com/web.config AND domain.com/portal/web.config ... so my domain.com/portal/default.aspx page will not load.

What is the real solution to this? Do I somehow find a way to merge my root web.config with my /portal/ directory web.config, or am I way off base here?

Any guidance would be greatly appreciated!