Your best bet would be to pull the remotes apart and check the serial port jack for cracked / cold solder joints. That error typically means that communications is occurring, but there's data corruption in the communications, such as a defective cable. In this case it seems more likely to be broken serial ports.

Has anything else changed, such as the PC or serial port you use for programming? Just want to make sure there's not some possible firmware differences between the remotes that could explain the issue.