I think it because there is only one source and they have gone offline. You can try right-clicking it and "find new sources" or download the "speed up crack" which essentially does this for you. You will only resume your download if the file comes online again (whether the original or an equivalent source). I would stay online (depending on how much you pay for your internet) with the speed up crack and hope the file comes up! Others may suggest going over to WinMX but I have found this to be even more tiresome when waiting for the file to become available.