How to trust a certificate for all users on a citrix server

Silly question: Are you running the command as an administrator? Only a user with local administrator rights can modify the machine stores. Windows 7 should elevate the mmc.exe process automatically, but maybe it isn't for some reason?

Also, you may want to try adding them to the Trusted Root CA folder instead. Maybe the changes will stick for some random reason...

I managed to solve a similar problem I was having by following the instructions here (here adapting steps 3 and 12 to read "Trusted Root Certification Authorities" instead of "Trusted Publishers"):

1. Download and save the certificate.
2. Open the Certificate Manager
   • Hit Windows+R, or click on the Blue Vista icon in the lower left hand corner
   • In the "Start Search" box, type "certmgr.msc" (no quotes).
   • The certificate manager will open.
3. Right click on "Trusted Root Certification Authorities" from the folder list on the left.
4. In the pop-up menu, choose "All Tasks" >> "Import.."
5. Click the "Next" button
6. Click the "Browse" button
7. Browse to the location where the certificate is saved, click on it then click the "Open" button
8. Click the "Next" button
9. Select "Place all certificates in the following store"
10. Click the "Browse" button
11. Put a checkmark beside "Show physical stores"
12. Expand the "Trusted Root Certification Authorities" folder
13. Click "Local Computer"
14. Click the "OK" button.
15. Click the "Next" button
16. Click the "Finish" button

Basically the bit I was missing when trying to import the certificate was to drill down into the "Local Computer" folder underneath the "Trusted Root Certification Authorities" folder.