NSAgent was installed in the default location (C:\Program Files\Altiris\Altiris Agent) then removed (aexagentutil /uninstallagents /clean) and re-installed to drive D (D:\Program Files\Altiris\Altiris Agent).
When Software Update Agent install policy came down, the task failed to start with exit code 1612.
In another instance return code (as per the logs), it returned exit code 1638.
Description: Starting SWD task: 'Software Update Agent Install' command line='msiexec /i Altiris_PatchMgmtAgent_Win32_6_1.msi /qn'
Description: Program 'Software Update Agent Install' completed. Exit code=1638
1612 The installation source for this product is not available. Verify that the source exists and that you can access it.
1638 Another version of this product is already installed. Installation of this version cannot continue. To configure or remove
the existing version of this product, use Add/Remove Programs on the Control Panel.
SUAgent 6.1. 1422
Patch Management 6.1