After calibrating the ESCs on my copter, I cannot communicate between my Laptop and the APM1 board. I have tried 3 PC's so far. 

When I try and upload the firmware to the copter I get the folling message: Upload succeeded, but verify failed: exp 0 got D at 253952 . I get the same message, with the same number every single time.

Also I am unable to connect to the board. When I try and connect I get the following message after the timeout times out: 

' Is your CLI switch in flight position? ' ( have verified that it is in the correct position, away from the Pins)

The error dialogue box also says ' System.Exception: No mavlink heartbeat packets where read from this port - verify baud rate and set up ' 

' It might also be waiting for GPS Lock APM planner waits for 2 valid heartbeat packets before connecting at ArdupilotMega.MAVLink.Open(Boolean getparams)      at ArdupilotMega.MainV2.MenuConnect_Click(Object sender, EventArgs e)

I have verified the COMM port settings as 115200, 8, none, 1 and for flow control, I have tried all three options as I read Xon/Xoff as a suggested solution in another thread. 

It also will not connect in terminal mode. 

Any help would be greatly appreciated as I have been stuck with this for two weeks now :(. 

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