There are two issues we've seen that give this error:
Scenario 1) While trying to run PMImport, it will fail to download AeXPatchDeployment.exe. Error in the logs indicates a file corruption: An error occurred while verifying trust for object 'D:\Program Files\Altiris\Patch Management\Downloads\Tools\AeXPatchDeployment.exe.TMP' (UnknownSubjectForm).
"Downloaded file has an incorrect or missing digital signature, previous version of the file will not be replaced. An error occured while verifying trust for object 'D:\Program Files\Altiris\Patch Management\Downloads\Tools\<.exe or .cab filename>.TMP' (UnknownSubjectForm)."
Scenario 2) We have also seen this error for customers that have purchased Windows 7 Extended Software Updates (ESU) if the information they were given for accessing the updated PMImport is not used correctly.
Scenario 1) On this scenario IPS detection on the firewall was blocking the download.
Patch Management 8.x
Scenario 1) Create a firewall rule or turn of IPS to allow server to download files.
Scenario 2) For Windows 7 ESU customers, please ensure the password is correct and the URL is correct for accessing the ESU PMImport. NOTE: the URL is Case Sensitive.