Unfortunately, its common for third party flashes to be incompatible with newer model Canon DSLR's. When a flash model is still in production, a firmware update may be developed, but a out of production flash may not work on newer bodies.
I've bought Sigma EF compatible lenses that became doorstops as well for the same reason, they did not work on Canon DSLR's and could not be updated. It was even worse for those who bought Quantaray rebranded Sigma lenses.
Tamron has not been hit so hard this way, they have had a couple of lenses with this type of issue, but Sigma's entire lineup would not work when the change from EOS film to EOS DSLR's happened. I had five Sigma's and a couple of Quantarays, and only one could be upgraded. I dumped the rest.