Hello Abhishek,
to your user status "Complete" I guess you had assigned the business transaction FINI, which require a Error Free document. That means that the System status I1030 (Contains Error) must be inactive to set the Complete status successful.
If you solve the error in the document, afterwards the I1030 should be deactivated automatically and it should succeed to set the document to user status complete.
Best Regards
Gerhard