That is an old version of PGP to be using with Outlook 2010. 10.1.0 is compatible with the following:
PGP Desktop for Windows has been tested with the following email clients:
¡ Microsoft Outlook 2007 SP2(Outlook 12)
¡ Microsoft Outlook 2003 SP3
¡ Microsoft Outlook XP SP3
¡ Microsoft Windows Mail 6.0.600.16386
¡ Microsoft Outlook Express 6 SP1
¡ Microsoft Windows Live Mail version 2009
¡ Mozilla Thunderbird 3.0
¡ Lotus Notes 7.04, 8.02, 8.5.1
¡ Novell GroupWise 6.5.3
I would suggest upgrading as a test to see if this fixes the issue, the latest version is 10.3.0 MP1