STM32 Discovery -- Requires Official ST-Link?
If the programmer works with other boards, the most likely explanation definitely is that you've got some connections missing (is the board powered?) or duplicate (external clone AND on-board programmer both connected at the same time) connections.

SWD is so simple and well-documented that there's no way you can actually include a lockout mechanism. The MCUs are designed to be programmed by any tool that speaks SWD and sends the commands given in the programming manual – STLink v2 actually refers to the protocol you talk between programmer and PC to make the programmer do the right SWD things.