Hey Naveen
This Issue looks completely strange, can you brief me up the issue by answering the following .
Is this happening with only one user or for all??? Is there any specific leave type that is causing the error? Have you checked the RPTARQPOST report? Is this scheduled as a background job?? Can you let me know what was the frequency applied for it.
Try executing the report manually & check with one scenario.
Hope this Info 
will be Helpful
Cheers 
Pradyp