If you run into an issue where you see an Unexpected EOF encountered in BCP data-file, it will be one of two things.
1) When you export out with Subset, and import back into a target database, we use the internal tools from Microsoft to generate the export (bulk copy). If you are importing into a different version of Microsoft SQL server, you will get incompatibility errors, including the Unexpected EOF error.
2) Along with the same version of SQL Server, make sure the database you are subsetting from has the exact same database structure as the database you are importing to. In this example, there was a new foreign key constraint on the target database that did not exist in the source database, which made the generated subset incompatible with the target database.
To confirm your database structures are the same, you can export the DDL for both the source and target database, and perform a diff on the DDL's to confirm if the structure is the same. If you are not able to do this, you should refer to your DBA on the structure of your source and target databases are the same.