New new security in IIS 7 blocks the download of CER files. To resolve the issue the following entry should be removed from all site servers with IIS7 on the Altiris Virtual App.
1.) Select Altiris Virtual Application in IIS
2.) Launch Handler Mappings
3.) Locate SecurityCertificate Entry
4.) Delete it.
5.) Confirm .*,application/octet-stream exists in MIME Types after change.