The caution sign appears to be an indication that the IDE could not identify the port by the vid and pid (see board unfo).
Also if you feel the issue is with V2 b7 then you should move to the latest. I think it is V2 b10 but I've not checked recently.
Compilation error: Error: 2 UNKNOWN: exit status 1
Have you investigated the lines before that error report? I've always found some hint or line to allow more in depth troubleshooting.
Quite honestly, if you through up your hands and ran to the forum providing the single line Error 2 UNKNOWN then respectively you should not be using a beta IDE.