I have a sandisk extreme 64gb, samsung evo 128gb, and a lexar 128gb 6xx which is the same type as the supplied card and they all say sd card error and cannot be formatted.

I have tried delete partitions, formatting fat, fat32 etc and they wont work, an older 32gb slow card works.

i thougth 64gb was supported, anyone got any ideas ?

64GB is supported, I think some 128GB might work but can't be utilized fully (maybe some future firmware update will address this)?

What do you mean when you say they "won't work"?

Are you formatting the cards in the Mavic?