We had never done any change to this for past 4 months, this job is failing now.
So what? The CA-7 schedule scan has little to nothing to do with the fact that the job is failing -- that is due to something else entirely. For example, if your job uses a data set but does not always open it, and your site standard is for HSM to delete data sets not used in 4 months, it is very possible that your HSM delete got rid of a data set and caused a JCL error in the job -- again, NOTHING to do with CA-7.
Why have you not looked in the CA-7 Commands manual at the syntax for the SSCAN command and figured out -- on your own -- that you (or someone with authorization at your site) needs to enter SSCAN,SCAN=LNG to reverse the effects of the SSCAN,SCAN=ABR command? And SSCAN cannot be run on a job -- SCHEDULE SCAN means that all jobs are scheduled.
The real way to solve your problem is to find out, by looking at the job output, what the problem is -- but as long as you want to mess around with CA-7 instead of addressing the problem, do so as long as you want.