Regarding write data to records.

I am getting weired error while saving data to records. I have a table which has onlly three not null column. I am passing values to all of them. But I am getting constraint violation error for createdby_tcxt which is not even not null. I passed value for it as well. I checked DB structure, checked records many times. Even I am getting data into the process model to update. The error is like " Data constraint or integrity violation: the createdby_txt field doesn't have default value. Anyone has any idea why I may be faving this issue.