Custom sharepoint timer job shows status as failed

Hi 

I have created one customer timer job

Its deployed and activated successfully.

But when it runs it shows status as -FAILED in central admin job status.

I am getting the follwoing log ,

The Execute method of job definition SP_MyJob_CustTimerJob (ID bc2a6067-44cd-4241-935e-9c2b7a835d35) threw an exception. More information is included below.  Object reference not set to an instance of an object.96c023ed-ffa3-442a-a858-1981208f2118

02/20/2014 03:54:16.24 OWSTIMER.EXE (0x1C2C)                  0x1B98 SharePoint Foundation         Timer                        72aeUnexpectedException stack trace:    at SP_MyJob_CustTimerJob.Execute(Guid contentDbId)     at Microsoft.SharePoint.Administration.SPTimerJobInvokeInternal.Invoke(SPJobDefinition jd, Guid targetInstanceId, Boolean isTimerService, Int32& result)96c023ed-ffa3-442a-a858-1981208f2118

I am not able to understand why its gettin failed.

I changed the Timer service account to my own account. restarted IIS and timer service redeployed the timer job but nothing happend .

same failed message.

Anybody got this type of issue ? pls suggest any solution.