I have a couple of STM32L476 mBed boards talking to each other. The development environment is Keil UVision. After some time one of the boards stops operating as expected. I then try to halt execution which seems to stop but no execution point is shown in the code. Pressing the next line, or jump out of buttons produces a message saying "Debugger - Cortex-M Error", "This target device does not support all the defined breakpoints! Please reduce the number of breakpoints and start again". I have tried this by pressing the "Kill all breakpoints" button and re-trying. The result is the same. The STLink reports hardware version V2-1 and firmware version V2J25M14. Any suggestions as to how I might get the debugger to function properly?