"Cannot get debug register" error message

Why am I getting a "Cannot get debug register" error message when I connect to the target?

CrossStudio displays this message when it detects an error while getting one of the target's debug registers. This could be caused by any of the following:

• JTAG/SWD clock is too fast for device - 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.
• Unreliable JTAG/SWD Connection - try reducing the JTAG clock frequency or reducing the target interface's cable lengths as much as possible.
• Incorrectly connected JTAG/SWD connection - see the pinout of the 20-way and 10-way ARM connectors.