TT rows do not contain the full data model like the DB rows. You will need to convert the ttJobMtlRow.Number05 or ttJobMtlRow[“Number05”] using the UDField method of the tt row objects. This applies to all UD fields setting and getting there are methods for them for the TT rows.
ttJobMtlRow.UDField<decimal>("Number05");
ttJobMtlRow.SetUDField<decimal>("Number05", 17.44M);
