Err99 and busy flash

Per the problem description, it seems the flash circuitry has a malfunction.

In order to perform a correct diagnostics and repair of it, it is necessary to open such camera and perform it by a qualified camera repair technician.

If it's under warranty, I do recommend you to send it back to make valid the warranty.

If not, then you have the options of pay for its repair, or do it yourself if you are willing tgo open it and perform some basic diagnostics of the failure. You will need tools to do it, which includes the usage of a soldering iron.

Best regards,