Not able to checkin project of different owners using psi

Hi All , 

I am updating the project custom fields using psi, after updation I wrote steps for checkout-update-checkin

In QueueCheckInProject, I am facing an issue. I am able to update and check-in the project only if the owner is same as the present user.If the owner is different its throwing an error .

For credentials , I am using - project.Credentials = CredentialCache.DefaultCredentials;

Error -  rojectServerError(s) LastError=ProjectCheckinFailed Instructions: Pass this into PSClientError constructor to access all error information .

what changes need to be done, Please help.

Indresh