You may be unable to launch a Classic Collaborate session using version 1.6.3 of the Collaborate Launcher.
The current workaround is to change your settings so that Collaborate .collab files are opened with Java rather than the launcher. There’s information and steps on how to do this on the Collaborate support site.
Blackboard have released an updated version of the launcher. Note that if you followed the instructions for the workaround, you will need to change the file associations back. More information.