" is not a valid integer value (RM Sort)

The green band suggests there is a problem validating the default form; oddly in this case the default was RM.  However, this was triggered by the inability to validate correctly as there was incorrect information provided.  As a result removed all populated fields and replaced one at a time to conduct a process of elimination.

Check preset info in Tools > Options > Master > RMSort.

Are all the DSAs and RM populated correctly: defaults in correct fields, Postal Area etc.?

This above query did not like the pre-entered Default Poster address.  UK Mail had 0000000000 default format instead of A123456.