The following text is the applicable content taken from the linked document:
This section describes error messages and what they mean.
- You authenticated successfully, but do not have permission to decrypt this message.
You do not have permission to decrypt this message. Or, the administrator has disabled your ability to decrypt the message. Contact your email administrator.
- You authenticated successfully, but the decryption key for your message has been deleted.
The decryption key for this message has expired or has been deleted. Contact your email administrator.
- There was a critical error processing your request. There may be a problem with the system or your request.
Proofpoint Encryption is temporarily unavailable. If this situation persists, contact your email administrator.
- The message you are trying to read is corrupted and cannot be processed. Please contact the sender of the message.
The message is corrupted and cannot be decrypted. Contact the sender of the message.
- The page you requested was not found. If you clicked a link to get here, click the Back button in your browser to return to the previous page.
The page you are trying to view in the browser is not available or does not exist. Click the Back button in your browser.
- The username you requested has already been registered.
You have already authenticated with Proofpoint Encryption.
- There was an error retrieving the key for your message. If this error persists, please contact your administrator.
The key server is temporarily unavailable. Try again later, and if you still cannot decrypt the message, contact your email administrator.
- Your account has been disabled.
Your email administrator has disabled your account.
- Login Disabled
You do not have permission to perform this action.
Error with Large HTML Secure Messages.
If your HTML message contains more than 500 KB of content, you may encounter a "Large Message Warning" error message. This limitation applies to Firefox 3.X or Internet Explorer browsers when you reply to the message or forward it. This limitation does not apply to plain text.
Intermittent Problem with Replying to or Forwarding Secure Messages
If Proofpoint Encryption hangs when you try to compose a message and click the Reply, Reply All, or Forward links, click Cancel and try again. If the original text of the secure message does not display in the browser, refresh the browser or close the browser and open it again. The behavior is infrequent, intermittent, and typically works the second time around.
If you use Outlook 2007 on Windows Vista.
Do not save the SecureMessageAtt.htm attachment to disk and then try to open it. Open it from the email message.