Result Codes:
11: Seg Fault
15: Executed Too Long
256, 512, 768, 1024: various errors in tester-# files (you should be able to run them on EWS and get the same error)
17408: Exceeded 2 GB
(More will be added as their meaning is discovered)

Is every test working on CONTEST except /bin/ls and all the tests are working on EWS?
For some reason, only /bin/ls has a problem with knowing which variables to use. If you are using generic variable names like "head", "tail", "front", etc, try renaming those variables (my_head, or whatever) and you should run fine on CONTEST. Otherwise, the /bin/ls program will overwrite your own variables with its code, probably seg faulting your code.