SSL certificate error

We have an SSL certificate for our www domain and want to use this in Icewarp unfortunately we always receive an error when we try to import it. 

SYSTEM [00007F927AAE9700] 06:56:47 Load key and certificate: PEM_read_bio_PrivateKey failed
SYSTEM [00007F927AAE9700] 06:56:47 SSL initialization Error: SSL_CTX_LoadKeyAndCertificate(/CN=usimail.ru, 4C:EA:60:00:2B:20:D7:67:6E:74:0C:C3:BE:0D:BF:D1:2E:7D:E0:B5) failed