ESC calibration issues (Velineon VXL-3s, throttle trim error)

I'm trying to calibrate a Velineon VXL-3s ESC with a Mega and for some reason it's giving me problems. The last VXL-3s I think went bad as it wouldn't accept a signal from the microcontroller to calibrate, and the new one gives me a blinking green LED indicating that the throttle trim is incorrectly set. Just like I've done many times before with the old controller, neutral is 1500 uS, full throttle is 2000 uS, and full reverse is 1000 uS, which has never given me an issue before when calibrating or operating. When connected to the pin set as neutral, and right after I enter calibration mode, it throws the error. Any ideas on what could be causing this problem?

Thanks in advance!