The OWA certificate error that you may get in your browser when trying to access your Outlook account through the web access interface is a very common error.
You need to install the certificate in order to access your account.
If you are having certificate issues when using Outlook Web Access, this next screen will probably look familiar to you:
It's your browser complaining about the security certificate on the mail server. What you need to do is click the "continue to this website" link and keep an eye on the area next to your browser's address bar:
it will show up in red with a message "certificate error". You need to click on the certificate error area next to the address bar which will result in this screen showing up:
Click the "View certificates" link at the bottom. Windows will then show this certificate information screen:
Click the "Install Certificate" button in order to proceed.
Note: if you are running Windows Vista, this button may be disabled. That's because you are not running Internet Explorer in "Administrative mode". Close your Internet Explorer and restart it by right-clicking your Internet Explorer icon and selecting "Run as Administrator".
Then repeat the previous steps up to here and continue by clicking on the "Install Certificate" button.
That brings up the certificate import wizard:
Click next to continue. Again, if you are running Windows Vista, make sure to select the radio button next to "Place all certificates in the following store" and click browse
Select the Trusted Root Certification Authorities and click ok (this screen looks a little different in Windows XP, but you'll have to select the Trusted Root Certification Authorities just as well)
After clicking the ok button, you'll see this security warning:
Confirm that you want to install the certificate.
Windows will show you a message that the installation was successful and you need to restart your browser for the changes to take effect.
You should now be able to use Outlook Web Access without the OWA Certificate Error.