Documentation talk:Blackboard Collaborate/Join a Web Conferencing Session

Verify Java is associated with JNLP files using the Java Control Panel window. Open it by clicking “Start,” selecting “Control Panel,” clicking “Programs” and clicking the “Java (32-bit)” option. Click the “Advanced” tab at the top of the Java Control Panel window, click the plus sign to the left of “JNLP File/MIME Association,” select “Always Allow” or “Prompt” and click “OK.” JNLP files won’t work if you select “Never Allow.” You can also use the Open With feature in Windows to associate JNLP files with Java Web Start. Right-click a JNLP file and click “Open With.” Select the “Java Web Start Launcher” application in the list or click “Browse,” browse to the “C:\Program Files (x86)\Java\jre[version]\bin” folder on your computer and double-click the “Javaws.exe” program file. Browse to the “Program FIles” directory if you don’t see the “Program Files (x86)”

from: http://smallbusiness.chron.com/open-jnlp-file-29082.html