Sentinel Pro is the so-called DONGLE (aka Hardware Lock) for 3DS. It is a piece of hardware that protects the software from being stolen. When somebody buys 3DS, he actually buys the DONGLE plus some disks and books. If the DONGLE is being lost/stolen/destroyed, you would have to buy a new copy of the program.

3DS checks for the dongle when starting and during the work. If it is not present or is being removed, the program quits. It is only possible to start 3DS in Network Slave mode without the Sentinel Pro, but you cannot model in Slave mode.

You have two choices: 1.Be a nice guy and buy the program 2.Be a bad guy and use a crack.

If you go the second way, here is the Answer to the Questions you would probably post next to this newsgroup:

Q:I get an "Invalid Normal Array" message Q:My meshes got destroyed, vertices go crazy Q:The lights go dark in the animation

A:You have a BAD crack of 3DS.