The current version of application manager has a bug related to certificate importing. A certificate will appear to import correctly, but will not work correctly. We are investigating the issue.
The workaround is to go to:
C:\Program Files\Microsoft HealthVault\SDK\Tools
and execute ComputerCertificates.msc. This will launch the MMC snap-in for certificates. To import a certificate, right click on "Certificates", "All Tasks", "Import...".