Sometimes ShapeShift takes down certain coins/tokens to perform maintenance and therefore making them Temporarily Unavailable. You can easily check that by going to https://shapeshift.io/, clicking on a coin icon in the Choose Which Assets to Trade box on the right and search for your target coin using the search field at the top.
If your destination coin (the coin you're shifting to) shows up grayed out and with a message TEMPORARILY UNAVAILABLE (screenshot below), this is the reason why you're getting that error message in Jaxx. Until ShapeShift re-enables that coin/token, you won't be able to shift to it.
We're sorry for the inconvenience and if you need more information on the coin you're trying to shift to and its availability, please reach out to ShapeShift directly: https://shapeshift.zendesk.com/hc/en-us/requests/new