Totus
1. Try to test if PGP is always running before Outllok. Run PGP again and then outlook, alwasy in this order.
2. Move encrypted message to PGP Viewer and test ifyou can open successfully and see the body.
3. Check if messaging flag is enabled on your key. Navigate to PGP Desktop and click on the Key > Key Properties > Key Usage and use small triangular on View to check if PGP Messaging is Enabled
4. What will happen if you try to reply to this message without body. Do you see body appears on reply.
Run a test and post a feedback.
5. Does it occur only for a specific encoded messages (like only with attachments) or does it happen only when the message is sent from the specific sender or simply it happens all the time.
6. Enable debug logs on your PGP Desktop
( I guess you use a Standalone PGP Desktop Client ) and post the logs, please.
Also if Standalone do you know how it was installed. Did you install with addtional switches ?
HOW TO: Add Debug Level Logging on Windows 7 for Symatec Encryption Desktop (previously PGP Desktop)
http://www.symantec.com/docs/HOWTO64205
7. Re-enroll the user and see if the issue occur
HOW TO: Re-enroll Symantec Encryption Desktop for Windows Clients
http://www.symantec.com/docs/HOWTO42029
8. Check this Microsoft Technet:
http://social.technet.microsoft.com/Forums/office/en-US/691e9843-4fff-418d-9682-371122be61ed/missing-body-text-in-outlook-2010-message?forum=outlook
Although it is not related when running a PGP but only on Outllook itself still worth checking is also as follow:
a) virus scanner - disable and test encrypted message
b) check message setting on Outllook related to - View settings, Encoding in the message
c) Outlook -> Tools -> Options -> Mail Format and removed the ticks from "reduce the file size of the message
HTH