Linear Position Move not working for Negative Travel

I am facing Issue where my axis does not move in reverse direction. I have a requirement to move the axis back and forth continuously. Currently am using Move Relative Command to move the axis to Hi Limit (18 inches) and Low limit (0 inches) with increment of say 0.5 inches each time.With this my Positive move works once but as soon as the axis reaches positive limit and now i command to move back to position (high limit-0.5) but it does not move at all and i can see the commanded velocity nearly equal to zero even i had requested velocity of 0.5.

Has the axis faulted out when you reach the limit? Check your status bits for the axis to see if you are faulted.
Check the Auto Stop configuration to see what happens when you hit a limit.