Scheduled Job Sometimes Error Sometimes Not

I have a scheduled job contain 2 steps. Step 1 is execute DTS Package
using CmdExec 'DTSRun', step 2 using TSQL to execute just simple query.
This job execute recurely every day, every 6 hours.
The problem is, sometimes this job was successfull, but sometimes
failed with error as below :

....
....
Process Exit Code -1073741819. The step failed.

Please help me, what the cause of the error?
Any help would be greatly appreciated.

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