This error might be caused by, well, the license file being missing. However, for many users, either tutorial was not followed correctly or the tutorial is not correct for their device. With 400+ Android devices (and growing), the iSyncr tutorial is not always accurate on how to set the device up. Unfortunately, manufacturers have chosen many different ways to put a device in "Mass Storage" or "Disk Drive" mode. In fact, some manufactures have even changed where the setting is in the menu from one software update to the next.
Our end goal is simple. Get the device in "Mass Storage" or "Disk Drive" mode. You may have to consult your user manual to do this. Some devices even need USB drivers to do this. Once done, the device should show up as a removable drive in Windows, instead of a device. Then you can simply run iSyncr.exe and quickly get your music onto your device!
Note: If you find that the tutorial (Help->Tutorial) is incorrect for you device, please let us know. You'll help lots of other people out.