I botched a show this summer, due to the same error message. I checked, and a card I had been using seemed to no longer work with the Tascam. I bought one from the approved list, and everything has been smooth sailing since then.
Lots of people are really upset at Tascam for not being more forthright with the information that the vast majority of SD cards will not work, or at least are less likely to work, especially running four channels, especially at 24/96.
On the other hand, I think there has been no reports of a problem with an approved card.