ITMS 7.6, 8.x
There is a pending package on the package server which prevents other packages from being downloaded.
At first we need to make sure that there are no pending packages on package servers. If any, we need to open the Altiris Console - Tasks tab and locate the task which is using the mentioned package and check the priority of the task. If it is set to High, change it to Normal. Then select "Go To Package" and for the package causing the issue, change the name and click "Apply". Then change the name of the package back and click "Apply" again. This will force the package update and regenerate snapshots.
If the priority is not the cause, change the option under the Package Servers tab of the package to "Package Servers automatically with manual presaging" and save the changes.
On the package server then click "Refresh Packages" and "Resend Package Status" in Altiris Agent - Package Server tab. Then open Control Panel - Scheduled Tasks and run "NS.Package Distribution Point Update Schedule" and "NS.Package Refresh" schedule. Wait until package servers update their configuration.
Then login to the package server, update configuration and check if there are no pending or retrying packages in Altiris Agent - Package Servers tab.
In some cases with more recent versions of ITMS, you can force the package to recheck if for some reason the package version gets out of sync.
Select the problematic package from the "Package Server" tab on the package server and click on "Check integrity"
After that, it may change to "Invalid" status.
Then, click on "Force Download" on the left menu options and it should change to "Valid" status again after the package is done verifying its contents.