The issue you are describing has the exact same symptoms as an AirPlay issue which was specifically corrected by the latest software (released on March 3). This Speaker software version should read as 7.2.37 in your SoundTouch app. Please follow the steps in this article to verify that you are currently upgraded to that exact version number.
Checking software version
Try temporarily disabling any other devices which might be automatically selecting the SoundTouch as an AirPlay destination. (Apple TV, Computer's running iTunes, other iOS devices.)
If you still run into the same message, we will next need to gather system logs from your SoundTouch 20 speaker. The procedure for getting log files can be found here:
Collecting system log information for SoundTouch™ 20, 30 and Portable systems
You can email those log files as an attachment to Technical_Support@bose.com Along with your forum Username (so that we can match them up with your post)