That error message sounds like the debugger is losing its connection to the RCM3400.
You might want to write a simple test program to run on your hardware to confirm correct wiring. Without multiple tasks, just open the serial port and relay data between STDOUT and the XT09. Once that's working, try to integrate that code back into your main program with the multiple tasks.
Other options: Can you just run Task1, with the other two tasks "on hold"? Can you single-step through Task1 using the debugger to see what's happening?
Based on the crash, you're likely overwriting memory, overflowing your stack, or possibly even reconfiguring serial port A (with a serAxxx call instead of serDxxx).