The thing I would suspect the most is the use of a System DSN - from Win7 forward our experience with System DSNs has been problematic. As long as users are being validated on the network (i.e. have a login generated on the domain controller), User DSNs work much more reliably. They are a pain to maintain of course, as when the user changes you have to be sure the new user has a DSN defined. Any other issue is going to be a challenge to identify.