This can be caused by a conflict with the in-kernel jsm driver, where it has claimed the adapter. Check to see if the jsm module is loaded:
# lsmod | grep jsm
If so, unload the module:
# rmmod jsm
The jsm module, should be renamed to prevent it from loading when rebooted:
#cd /lib/modules/`uname -r`/kernel/drivers/serial/jsm
# mv jsm.ko bak.jsm
The system should be rebooted in order for the jsm driver to relinquish control so the dgnc driver can claim the adapter.