"Best Practice: Managing Task Server Communications in 7.0 and 7.1"

http://www.symantec.com/docs/HOWTO48411

The 5 invalid packages are from Deployment Solution, if you configure DS correctly they should populate, if you don't need DS it doesn't matter.

There are filters (Filters > Computer Filters > Task Service Filters) in the console that tell you how many Task Agents are connected to each Task Server, you can use the <NSName> one as a target for a Task to reset task agent and run that weekly.