If you happen to have jD Long-range modem sets or another type FTDI adapter set that does not work properly with your computer (especially windows).
Please take a look at FTDI Corp Technical Note TN_165 dated 2016-04-05
jD-RF900/868 sets are using original FTDI chips and FTDI Corp. is trying to limit amount of illegal china copies, you need to update your drivers on windows computers to make them work properly again.
Latest driver can be found from their website here:
http://www.ftdichip.com/Drivers/CDM/CDM21216_Setup.exe