Is there some limitations.. What are the known problems...
Does it mean, for instance, VISA is now the version with 8.6, and that I have to validate all my existing VIs in 8.5.1 once I install 8.6 on the same computer.
You can have as many versions of LabVIEW installed that you want. However, you can only have one driver version. You don't have to install the latest verison of a driver though. Driver versions and LabVIEW versions are somewhat independent anyway. Even if you did not install 8.6, you can update and often should update your drivers.
If you are concerned about driver/LabVIEW compatibility across different LabVIEW versions, you can always check the readme files to see which LabVIEW versions are supported by the driver. To reiterate what Dennis said, don't install multiple versions of drivers, but you can have as many LabVIEW versions as you wish on one computer.
Cheers,
Marti C Applications Engineer National Instruments NI Medical
