FreeRTOS on PIC 18F8722

I am trying the demo programs on a PIC 18F8722 on a CCS development board. I have programs 1 and 2 (blinking LEDs) running, but the third (serial i/o) resets on receiving serial input.  The problem appears to be in the task switching within the serial ISR; if a character is received while the input task is blocking on the queue, the program counter goes awry. I have changed the amount of memory in the context save/restore functions per the instructions on the web site, but nothing else related to context or interrupts. Can anyone offer help or suggestions on what to try next?