Hi,
Thank you for persevering with my suggestions.
As your speaker seems to work OK when using the aux input but not when using the BT, my suggestions now are:
1. Try connecting and switching on, the AC adapter to the speaker and then connecting it to a BT source and see if works OK.
My thoughts on this are that using the BT requires more power than when using the aux input, so this test is just designed to eliminate the speaker battery as the potential source of the problem.
2. Ensure that any other BT capable device within range has its' BT disabled so as to eliminate any potential BT conflict as the source of your problem. It may be advisable to do this in conjunction with the test above. I realize that your speaker is capable of 'handling' two BT devices at once, but to find the problem, is a process of elimination. What works and what doesn't work.
If the above fails to find the cause, then to me, as obvious as it sounds, it seems there is a problem with the BT in your speaker. Unfortunately there is no information available which could allow for more ways to conclusively prove this, such as reloading the 'firmware' in the speaker in case it is corrupted or even resetting the speaker back to a 'factory default' state as you can with mobile phones to prove whether it is a hardware or a software problem.
How long have you had the speaker?
There is a 12 month manufacturer's warranty on your speaker if you are in the USA and a 24 month warranty if you are in the EU. If you have had the speaker for less than this period of time then I suggest that you consult the warranty information that came with the speaker documentation as to what you have to do to make a claim for a warranty repair or replacement.
If you have had it for just a bit longer than the warranty period, say just a month more, I would still contact the manufacturer anyway and tell them of your disappointment with their product etc., and ask if there is anything that they can do to help you. It never hurts to ask and the worst that they can say is no.
If you cannot find the warranty information here is a link.
http://support.creative.com/warranty/welcome.aspx?pid=21606&cid=1&h=2