I don't have a good answer. I have a few questions that might provide us a clue.
Do the adapters have any error in the device log?
Any entries in the event log that might be related?
What operating system and service pack level was installed on the systems where the network adapters were working? Is there something different about the cables or the switch on the system where they are not working?
What is the value for the hardware Ids for the adapters? (From Windows Device Manager --> Details Tab -->Property:Hardware ids) and what is the driver date and version? The only driver for Windows Server 2008 R2 and those adapters is the one Microsoft provides as part of the OS. I am curious to see if the adapter's hardware ids are being identified correctly, which affects loading the right driver in Windows.
Is SP1 installed (or not) on the system where the adapters failed?