The team at Plogue have found a bug affecting those wanting to use ReWire devices with Pro Tools 11. They write;
“I figured out the issue, this is a major bug with Pro Tools 11. ReWire devices are only scanned when the DigiReWire plugin is scanned (which typically happens when running a new Pro Tools version). Any ReWire device installed AFTER that scan will never show up in Pro Tools 11 until a new plugin scan occurs.
On OS X, this can be forced by manually deleting the file name “InstalledAAXPlugIns”
in <your user>/Library/Preferences/Avid/Pro Tools
If the issue also occurs in Windows, there is most likely a similar file.”
If you are having problems installing ReWire devices, this may well be the issue.