Unable to install music at the moment, try again later on iPod Touch

3 in the last few month

I come in having been listening to music on my Ipod Touch, and put it on Charge.

The charging cable is connected to a USB power point not a computer (because plugging it in to a computer to charge risks it deciding not to charge until you have logged in, unlocked the Ipod and positivley identified it) and Wifi is turned off. A couple of days later when I go out again I unplug the Ipod, but when I try to start playing music I instead get a message "unable to install music at the moment, try again later"

1) How can I prevent this from happening

2) When it does, how can I fix it given that I am now out and not able to connect to my WiFi

3) Why is the Ipod trying to (re)Install music - I've not told it to uninstall it

[Re-Titled by Moderator]