Well I had contacted Horizon and asked them for a manual, or any info on flashing lights on the ESC, and got this reply.
The Flashing Green light is a Failed Self Test and in most situations will need repair or replacement.
Best Regards,
Jason
Product Support
Air and Surface Specialist...
It may be a bad ESC, but it's hard to say without finding an actual manual for the ESC. How long ago did you buy it? If it's still under warranty, Horizon will replace it.
Try doing a factory reset and see if that fixes it. You have your throttle trim at zero when turning the radio on right? I can't find any info on the BLX100 (assuming your ESC is stock) with regards to flashing light sequences and what they mean. Typical for Spektrum electronics.