As far as I can tell, Poweramp behaves this way by design; it "phones home" every three days. You will only get a message if you have no active Internet, since if you don't, it can't validate your license. If your Android is a cell phone this isn't an issue, if it's a music player and only needs Internet via WiFi to use the Google Market, then it can easily become a problem, especially if you take your player with you on say a long trip where your access to WiFi hot spots is limited.
Unless you are saying something different? The only way I have read to stop this license check behavior is to root your device and run a patch program that patches (or cracks) Poweramp to stop the license check.
I can only say i can run poweramp even in air plane mode now. I am on jb on my phone. N tat previously there was this issue reported on gingerbread.
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