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.
SUAgent uninstall does not completely clean the registry so that future SUAgent installations to an alternate location can be performed. If you uninstall the SUAgent using "msiexec /x Altiris_PatchMgmtAgent_Win32_6_1.msi /qn" or if you uninstall all the agents using "aexagentutil /uninstallagents /clean", there is a registry key that is left behind which points to the previous location of the Altiris_PatchMgmtAgent_Win32_6_1.msi file.
The following are descriptions of MSEXEC return codes 1612 & 1638:
ERROR_INSTALL_SOURCE_ ABSENT 1612 The installation source for this product is not available. Verify that the source exists and that you can access it.
ERROR_PRODUCT_VERSION 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.
By removing this registry key, you can re-install the SUAgent through client policies, if the NSAgent was previously installed on a different drive: