Symantec Management Agent Task Status is Shutting Down and Task Server: field is blank
In addition to the Classic .NET AppPool there was another corrupt non-functioning app pool Classic .NET AppPool". (hint: extra quotes at the end of the name).
The corrupt app pool was not listed in the application pool list however the Default Web Site and Altiris Client Task Server virtual directory were pointing to the corrupt pool.
Change Default Web Site and Altiris Virtual Directory app pools to use Classic .Net AppPool
Windows 2008 R2 Task Server
ITMS 7.1 SP2 MP1.1