Mike, thank you for your quick response and help, it is VERY much appreciated! ok here is my web.config with the 500 error
<!-- forms or Windows authentication -->
<authentication mode="forms">
<forms name=".DOTNETNUKE" protection="All" timeout="60" cookieless="UseCookies" />
</authentication>
<identity impersonate="true" userName="manning-napier\ssantacr" password=”T45qwz567”/>
<!-- <authentication mode="Windows">
</authentication>
-->
When I change it to this I can log in either thru a DNN user or an AD user (but not automatically which is what I'm tryin to do!)
<!-- forms or Windows authentication -->
<authentication mode="forms">
<forms name=".DOTNETNUKE" protection="All" timeout="60" cookieless="UseCookies" />
</authentication>
<!-- <identity impersonate="true" userName="manning-napier\ssantacr" password=”T45qwz567”/>
<authentication mode="Windows">
</authentication>
-->
Finally I looked at my app pools. I have both the "Classic .Net AppPool" and "DefaultAppPool" started. For the fun of it I tried stopping the "DefaultAppPool" and then I got a 503 Service Unavailable error. So I think I'm ok in that department leaving both of them running...