Posted this issue in the blog but though it might fit well here in the Forum.

Problem
I initially logged the issue we were having working with the latest 15.1 release. The issues presented itself when using an existing DB and upgrading in a test environment. Installing with a demo database worked fine but using a 15.0 DB and upgrading presented this .net error trying to load the web view (Shown below). The error indicated it could not find the site map node. This turned out to be misleading. After many installs and re-installs on both a demo and upgrade I resolved the issue.
Solution
I found by running a trace while trying to load the web application in both systems demo and upgrade that a specific query was not returning any rows in my upgraded DB. The query was looking for a GUEST user in the database which does not exist in my upgrade system. Another interesting thing is the demo database seems to actually run a different query, I believe based on the license that is installed, making it preform differently then the upgraded system. The query was looking to join users and usermain looking for the GUEST user which my upgrade database did not have. I am not sure if this is normal or just my situation but thought i would share the information here.

Error Details
Exception Details: System.ArgumentException: Could not find the sitemap node with URL 'http://ecm-test/imis15/Admin/?hkey=6edd071c-aeca-42f5-847e-3e7aabea2a6b'.
Source Error:
An unhandled exception was generated during the execution of the current web request. Information regarding the origin and location of the exception can be identified using the exception stack trace below.

Stack Trace:
[ArgumentException: Could not find the sitemap node with URL 'http://ecm-test/imis15/Admin/?hkey=6edd071c-aeca-42f5-847e-3e7aabea2a6b'.]