Why am I getting error- You must provide a transaction number?

Summary:

The whole error is as follows: You must provide a transaction number if the transaction source indicates manual transaction numbering. Otherwise don't provide a transaction number.

The transaction Source:

is enabled for auto numbering:

In the autoinvoice lines, I can see the TRXNUMBER also auto populated from source.

I have tried deleting the TrxNumber and Submitting the Autoinvoice program- that also has not worked. I end up getting upload error:

"The line cannot be updated or deleted because these operations are not allowed because the line has an Interface Line Context equal to ::: CONTRACT INTERNAL INVOICES"

If query the source 'CONTRACT INTERNAL INOVICES'- i see that this is disabled for auto- numbering