Closed Unassigned: MAPI_E_FAILONEPROVIDER on logon [17704]

I've started getting this message recently when trying to open a store in online mode.

Code: MAPI_E_FAILONEPROVIDER == 0x8004011D
Function CallOpenMsgStore( lpMAPISession, (ULONG_PTR)m_hWnd, lpEntryID, ulFlags, (LPMDB*)lppMAPIProp)
File MainDlg.cpp
Line 435