I saw a problem yesterday with a WebServices REST (v3.3) job. The job was ending with the status FAULT_POST_PROCESSING, and these error messages:
U00021719 Syntax error in object 'UC4.SCM.V140.DEPLOY.OI.DEPLOY.JOBS_REST', line '00000'.
U01001307 A variable name with the length 0 is not allowed.
Obviously, line 00000 makes no sense, and commenting out the entire post process did not resolve the problem. After some more tinkering, I discovered that the problem lay not with the Post Process tab of the job, but with the Response section of the Web Service tab. Under the Response section, in the Headers tab, I had defined a single entry to take the content of one response header and store it in a variable. It initially looked okay, but eventually I discovered that the variable name needed to be specified without the leading ampersand (&) character.
It would obviously be preferable if the Automation Engine returned a more informative message in such situations.
It would also be nice if the WebServices REST documentation mentioned that the leading ampersand should be omitted.