Had the same problem yesterday. On OmxplayerBuilds I found the reason why. The firmware does not correspond to the version of omxplayer. I solved it by downloading rpi-update (not raspi-update that comes with raspbian) and run rpi-update. It downloads the latest firmware and after a reboot some things improved like: omxplayer works again, mounting a USB-HD (1,5 TByte) is much quicker.
You can also try to downgrade to the previous version of omxplayer.