If you request too many active hardware-assisted breakpoints and watchpoints, you will see this error message:
Stopped; cannot insert breakpoints.
You may have requested too many hardware breakpoints and watchpoints.
This message is printed when you attempt to resume the program, since only then gdb knows exactly how many hardware breakpoints and watchpoints it needs to insert.
When this message is printed, you need to disable or remove some of the hardware-assisted breakpoints and watchpoints, and then continue.