I don't beleive "Program Files" have any affect here, neither the custom location. SMA and PS are working from default and any custom locations as well.
I beleive here are problems with connectivity to PS or the accessing the drive. Too less logs are provided in order to make an exact decision. From what is provided I see that this is an agent and it can't download the snapshot file from the Package Server. Since this agent got the PS codebases - means PS do have the package downloaded and Ready, and status updated on the Notification Server. The error is "0x80070057" which means "The parameter is incorrect". This error appears when creating a file with invalid name/path, or disk operation fails by other reason.
What you can try to do:
1. Check that target location is OK (ACL permissions, ability to create files on it). For SMA, the SYSTEM user should have full access to this location. According to your logs it will be something like: "x:\WINAPPS\Altiris\Altiris Agent\Agents\SoftwareManagement\Software Delivery\{87AB3970-9488-458C-B177-3EC73E09DA1E}\
2. Delte the package artifacts from this agent (the GUID folder mentioned in point 1) and try to download the package again.
3. Check whether HTTP/HTTPs transfer is working OK from that Package Server. Althought the methods of getting the package are different for HTTP and UNC, the target location is always the same. So if HTTP is working then the problem is not with the local Agent and it's custom location, but rather with UNC access to PS.
P.S. Could happen that you will need to reset server profiles through SMA Diagnostics window, since if too many errors will be stored for UNC path of the PS, it won't be selected by SMA anymore while next download attempts.