Re: VM translator passed all tests but when i submit, the grader says it failed
There's no way for us to possibly know the answer to that.
Have you asked the grader?
It is impossible for any set of tests to completely test any piece of software beyond a certain level of complexity -- for instance, even if you could do one billion tests a second, it would take over five centuries to test every possible result of a 32-bit number added to another 32-bit number. So the grader may simply have additional tests that you don't have and it is failing them.
Or they may have done something wrong in grading it.