Nios II application hang/lockup with an exception

Hello,

One more update. When the code was changed from:

altera_avalon_fifo_clear_event(FIFO_CSR_BASE, ALTERA_AVALON_FIFO_EVENT_AE_MSK);
altera_avalon_fifo_write_ienable(FIFO_CSR_BASE, ALTERA_AVALON_FIFO_IENABLE_AE_MSK);

to:

// FIFO_CSR_BASE = 0x610020
// ALTERA_AVALON_FIFO_EVENT_AE_MSK = 0x08
// ALTERA_AVALON_FIFO_IENABLE_AE_MSK = 0x08
OS_ENTER_CRITICAL();
altera_avalon_fifo_clear_event(0x610020, 0x08);
altera_avalon_fifo_write_ienable(0x610020, 0x08);
OS_EXIT_CRITICAL();

It failed one statement earlier in the assembly code per the address from ea-4, which is shown below:

Any supports are very appreciated!

Patrick