"Cannot identify target" error message

Why am I getting a "Cannot identify target" error message when I connect to the target?

CrossStudio displays this error message when it gets a JTAG device ID of 0x00000000 or 0xFFFFFFFF. This could be caused by any of the following:

• You are connecting to a target that requires adaptive clocking with a target interface that is not configured for adaptive clocking and is running the JTAG TCK too fast for the target. This typically happens with synthesized cores such as the NXP LPC2000.
• The JTAG clock frequency is too high - try reducing the JTAG clock frequency.
• Your current active project does not target the hardware you are trying to connect to and/or the project's Target > ARM Debug Interface project property does not match that of your hardware.
• The target is not powered.
• The wrong JTAG target interface type has been selected - make sure the target interface you are trying to connect to is actually physically attached to the hardware.
• The JTAG interface is not correctly connected to the target.
• The target is being held in reset.
• A program running on the target has disabled the JTAG pins or reconfigured them for an alternative function.
• The device is one of many on the JTAG scan chain and the JTAG Data/Instruction Bits Before/After project properties have not been set up correctly.