a) This is an indication that Mathias stopped at an address that could not be referenced back to a source line. This can happen if the code is "off in the weeds". It can also happen if your compiler linked in libraries and you happened to HALT the processor while it was executing code in one of these routines. You can open the CODE window and see the address and disassembly of where it is executing. You can continue to single step from the CODE window until you hit a source line (as evidenced by the green bar reappearing in the source window).

b) See FAQ4 Part A about landing on the wrong code page.

c) See FAQ3 Part B about mis-configured device types.