Since you said earlier that this is in a batch file, you need to look at checking the errorlevel in the batch file. See a similar discussion in this thread:

http://www.sqlservercentral.com/Forums/Topic1735929-23-1.aspx

Keep in mind that when calling sp_start_job, the return only tells you if the job started and that's all. If the job starts, it succeeds, if the job doesn't start it fails. If the job itself fails, it will not know.

Sue