After an OS X upgrade to Mountain Lion you may lose connection between your USB transmitter and your speaker when your Mac wakes up after sleep mode.
The solution is to remove and reinsert the USB transmitter. This issue only applies to Mac computers using OS X Mountain Lion.
We are currently working on a solution with Apple and a future driver update is expected to be released through Apple Software Update. Until then please remove and reinsert the USB transmitter to reestablish the connection between your Mac and Libratone Beat after sleep mode.