I had the exact same problem in Outlook 2010 64 bit.

It seems to occur if you had something that was previously signed in an earlier version of Outlook for 32 bit.

Here is the procedure I used to fix it:

• Back up all your code / projects etc.
• Close outlook.
• Search for VbaProject.OTM (or whatever file is used to store your projects, there may be more than one)
  For me it was in [Drive]:\Users\[Username]\AppData\Roaming\Microsoft\Outlook
• Move this file to another location.
• Open outlook.
• Go into VBA and recreate your projects from your backups.
• You should now be able to bring up the digital signature option without it crashing.

Hope that helps.

OUTLOOK 2013 VBA 崩溃 证书