From the Furthur web site:
"Due to unforeseen circumstances, Furthur regretfully will be unable to appear as scheduled at BottleRock Napa Valley on Thursday, May 9. Grateful Dead & Furthur Co-Founder Bob Weir, is unable to perform in any capacity for the next several weeks.
Furthur featuring Phil Lesh & Bob Weir look forward to returning to the road as scheduled on July 11 in Brooklyn for their Summer tour, which carries them through early October on the West Coast"
Hmm. Hope we find out what is going on.