Why the Java object was gone?

I submitted an job at 5:00am. Usually it takes 25 mins to run.

But last thursday, it took about 6 hours and status was still "Running".

I deleted it from History page.

System gave me an one line error that I didn't write it down then it deleted everything from History and the Java object itself.

Don't understand why it had happened.

Where I should go to check? and how?

Thanks,

Ivan