If you define APM monitoring for a Web Application named root, say Default Web Site/root, you fail because of an issue (or bug) in APM.
In the normal case APM creates a web-application-specific set of instances of the.NET Apps performance counters. This happens as soon as the first request is processed by the application (after proper configuration of course).
If your application is called:
Default Web Site/xyz
you’ll get .NET Apps counter instance:
_LM_W3SVC_1_ROOT_xyz
However, if your web application is named root, the performance counter instance:
_LM_W3SVC_1_ROOT_root
is never be created.
My guess because of an APM bug related to string manipulation (the two times root?).
The issue is also present for deeper nested sites like Default Web Site/SomeVirtualDirectory/root
This issue was discovered in SCOM 2012 R2 UR4.
I will run a MS support case on this