MultiTasking with RoibotC

I got bug with following program and then i do some modification but bug still exist.
In fact, How to do multitasking??


task one()
{
}

task two()
{
}

task three()
{
......
StopTask(2);
}

task main()
{

StartTask(one);
StartTask(three);
StartTask(two);

}

//Modified:
task main()
{

StartTask(one);
StartTask(three);
StartTask(two);
wait1msec(20000)
}

task main()
{
while(true)
{
StartTask(one);
StartTask(three);
StartTask(two);
wait1msec(20000)
}
}