Loose Connection to Usb Drive


I have a 3rd party (Apacer) USB pen drive hooked up to my PowerMac. For some reason some 5 - 10 times a day the connection to this drive fails; I see the 'spinning' whenever I try to connect to it in an application. The only solution is to unlug the USB stick and plug it back in (eject doesn't work). In some cases this causes problems with the application (e.g. Mozilla Thunderbird).
Is there any clue to how/why this happens?