I have
one VE849 transmitter and two receivers. When I try to pair my transmitter to the
two receivers, it says pairing failed.

Only one receiver can be powered on when it's being paired with the transmitter

therefore disconnect power from the one unit before trying to pair the second unit 

and then power off the paired unit and pair the remaining unit.

NOTE:One receiver will have the same serial number as the transmitter (the receiver 

that came in the same box as the transmitter), pair this one first.

If the pairing failure still exists, please contact ATEN Tech Support.