Flash Wont' Fire ERR 50. Pops up though, but wont fire

Hi, Some month ago My Canon eos 7d Stopped firing the flash. There’s No obstruction cuz the flash pops up. But on the display gives me the “busy” message, and won’t led me shoot (error 50)

When using external flash (hot shoe mount) everything works.

Tried with no success:

turn off, remove battery

Try other batteries

Firmware Downgrade + upgrade

Any DIY Fix Idea other that sending to service?