The error message occurs due to any of the following reasons:

• The status of Email Encryption Client (TMEEC) email address registration was not completed.
• The Outlook Add-ins is not loaded correctly on the user's machine.
• The Outlook Add-ins is not installed correctly on the user's machine.
• The mapi.dll file is corrupted.

To resolve the issue:

1. Make sure that the status of TMEEC email address registration is "Protection Complete", click My Private Address on TMEE tray tool menu to confirm the registration status and then complete the registration.

    

   If the registration status does not show "Protection Complete", refer to this KB article: Roamed status appears during Encryption for Email (TMEE) registration.

2. Make sure that the Outlook Add-ins are correctly installed and loaded. Private Post and Private Post Attachment should be in the list. To check, do one of the following:
   • For Outlook XP or 2003, go to Tools > Options > Other > Advanced Options > Add-in manager.
   • For Outlook 2007, go to Tools > Trust Center > Add-ins. Select Manage: COM Add-ins, and then click Go.
   • For Outlook 2010 or 2013, go to File > Options > Add-Ins. Select Manage: COM Add-ins, and then click Go.

3. If the Private Post and Private Post Attachment are not loaded, check the registry key value of "LoadBehavior" on the paths below, if there is an existing key and its value is unequal to "3", modify the value to "3". Finally, open the Outlook.

   • HKEY_CURRENT_USER
     [HKEY_CURRENT_USER\Software\Microsoft\Office\Outlook\Addins\PPOutl.Connect]
     [HKEY_CURRENT_USER\Software\Microsoft\Office\Outlook\Addins\PPOutlookAddIn.Connect]\

   • HKEY_LOCAL_MACHINE (32-bit):
     [HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Office\Outlook\Addins\PPOutl.Connect]\
     [HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Office\Outlook\Addins\PPOutlookAddIn.Connect]\

   • HKEY_LOCAL_MACHINE (64-bit):
     [HKEY_LOCAL_MACHINE\SOFTWARE\Wow6432Node\Microsoft\Office\Outlook\Addins\PPOutl.Connect]\
     [HKEY_LOCAL_MACHINE\SOFTWARE\Wow6432Node\Microsoft\Office\Outlook\Addins\PPOutlookAddIn.Connect]\

4. If the Private Post and Private Post Attachment are not listed, register the plug-in:

   1. Close the Outlook.
   2. Open the command prompt as an administrator then go to the TMEE installation folder. By default, it is \Program Files\Trend Micro\Email Encryption Client\Bin\ or \Program Files (x86)\Trend Micro\Encryption for Email\bin\.
   3. Run the command "regsvr32 ppoutl.dll". The "ppOutl.dll has been registered successfully" message should appear.
   4. Run the command "regsvr32 PPOutlookAddIn.dll ". The "PPOutlookAddIn.dll has been registered successfully" message should appear.

5. Ensure that the mapi.dll file is not corrupted.

   1. Close the Outlook.
   2. Open Windows Explorer and go to C:\windows\system32.
   3. Double-click fixmapi.exe.