This is not a recent problem, but given I have stumbled upon it twice in the last week I thought I'd share the problem and solution with the community here, specially as the 2 cases I had were becoming critical as package distribution was not working.
So, what is the issue? Well, first packages are not synchronising between the Notification Server (6.0 SP2 R13) which is a problem - specially in the week after MS12-020 was released).
What is blocking the package delivery? Honestly I can't tell. However the common point between both cases was that the packages where delivered on the PS under the "Altiris Agent" directory, with one guid per package.
As I couldn't get the package servers to synchronised I went to a random package and removed the Package Server Download Alternate Location entry. After running a client configuration update the package server started synchronising all packages.
This was true for both customers, and is...