What is the code you are using to set the UD field on the tt table?
From the ICE guide …
- Method directives work with temporary (tt) tables using tablesets, and so you access them through different syntax. These tablesets are defined in the business object’s (BO) contract .dll file, so their format is fixed and they are not regenerated with the data model. When building a method directive that refers to user-defined fields in temporary tables, reference them using the [“UDField<>()”] syntax. For example:
ttABCCode.UDField<System.String>("MyNewColumn _c")