Unable to open Entrust encrypted messages from Virtual Vault if the items are not in the content cache.  

A client trace reveals the following:

EVMSP: <message title> [Message::OpenAttach] Enter
EVMSP: <message title> [Message::OpenAttach] Exit: MAPI_E_NO_ACCESS
EVMSP: <message title> [Prop<struct IMessage>::GetLastError] Enter
EVMSP: <message title> [Prop<struct IMessage>::GetLastError] hResult: MAPI_E_NO_ACCESS
EVMSP: <message title> [Prop<struct IMessage>::GetLastError] Flags: 0x80000000
EVMSP: <message title> [Common::GetLastError] Enter
CL10N::GetTranslatedMsg
CComAutoUnlock<class ATL::CComAutoCriticalSection>::CComAutoUnlock
~CComAutoUnlock<class ATL::CComAutoCriticalSection>::CComAutoUnlock
CComAutoUnlock<class ATL::CComAutoCriticalSection>::~CComAutoUnlock
~CComAutoUnlock<class ATL::CComAutoCriticalSection>::~CComAutoUnlock
~CL10N::GetTranslatedMsg
EVMSP: <message title> [Common::GetLastError] Last error was NoAccess which can have multiple reasons many of which are quite normal for the EVMSP ranging from policy denying writable operations to the fact that archived items cannot be modified. If necessary, check more detailed EVMSP logging for the actual reason that the error was returned to the caller.
EVMSP: <message title> [Common::GetLastError] Returning text: You do not have permission to perform this Enterprise Vault operation.
EVMSP: <message title> [Common::GetLastError] Exit: S_OK