what problem winavr?

[kang2008]

void uart_reset(uint8_t port,uint8_t bit)
{
    asm volatile ( "cbi %0, %1" "\n\t"          \
                   : /* no outputs */           \
                   : "I" (port),                \
                     "I" (bit)                  \
                 );
}      

uart.c:162: warning: asm operand 0 probably doesn't match constraints
uart.c:162: warning: asm operand 1 probably doesn't match constraints
uart.c:162: error: impossible constraint in 'asm'

what 's error in the winavr?

thank you.