We have five small branch offices. Each branch office has a Zen FTTC fibre internet connection and a Draytek 2862 (running on the latest 3.9.0_BT firmware).
We have successfully imported our companies wildcard SSL certificate (issued by Godaddy) on to two of the five Drayteks. The other three Drayteks refuse to accept the same wildcard ssl certificate giving a error "Upload Fail ... The imported file format is wrong or password is wrong. Try again!!!!!!!!!!"

All five Drayteks were purchased at the same time. They're all the same model and with exception to the LAN and WAN settings they are configured exactly the same as each other. We have tried factory resetting the three problematic Draytek but they still refuse to accept the SSL certificate. The first two routers accepts the PKCS12 certificate without any problems. I have even separate the certificate using OpenSSL and tried applying the certificate and private key separately, but again this fails.

Any suggestions or advise would be appreciated.

Are they also all on the same firmware ?