What does the canSubmitToWorkflow() method has in your case? If you are checking the status here, then update the status when ever the customer record is updated.
That is a different error , doesn’t looks related to original post.
Try to debug and see why it is trying to creating a record in TaxInformationCustTable_IN, if you already have an existing record.
but while trying to edit master details i am facing that error.
the record was not there in taxinformationcusttable_in.
I already debug the code but i could not find any related information.
is this error related to any setup? or functional?
This looks like a data issue. You might be having a record in TaxInformationCustTable_IN without a value in custTable field. If so delete that record and try updating the customer.