Hi Nara,
You were not able to find enough information for your BT device on ni.com because LV supports mainly the BT devices that are supported by Microsoft. It looks like that D-link DBT-120 is one device that does not have full support.
From what Fandoid said in the
BlueTooth Discussion Forum it looks like if you install the MS Q323183 update and then install some BlueTooth Monitor.
I think the development kit he is refering to is located at
http://www.blu2i.com/downloads/ (found from Google.com)
You can get the DBT-120 driver from
D-Link DB-120 pageI am not very sure why this is happening but would definitely suggest referring to the above discussion forum post and try out the suggestions provided.
I hope this helps,
Ankita