Back ground job not finshing

hie gurus , i need help . i created a background job to run my program which creates material via bdc call transaction.

the job runs every 30min , how ever its not finishing processing and the program is not creating material and restarts after 30 min again so i now have a list of active jobs that are not finishing in the job overview. how ever if i run through debugger using JDBG the program runs through with no errors. any 1 have an idea as to what the problem could be.