Simon,
Please refer to these documents as well for information about other causes of this error.
http://digital.ni.com/public.nsf/websearch/2C99F5D635AE184C86256CD1005BBF65?OpenDocument
http://digital.ni.com/public.nsf/websearch/862567530005F09C8625677800701946?OpenDocument
http://digital.ni.com/public.nsf/allkb/64F59210BE983DAA86256F1A00006160?OpenDocument
Eli S.
National Instruments
Applications Engineer