The problem is most likely that when you made the schema, the sample rows used to define the column types saw a simple 5 or 9 digit character string as the entry and set the type to double. However, since your data has zip codes with the dash or space character, conversion to a numeric can't happen.
You need to remake the schema making sure the sample data contains a zip+4 entry so that this column is typed as a string. I frequently just add the -nnnn to the zip values in the first couple of rows, make the schema, then re-edit the Excel file.
Then within Expressor you can decide whether to throw away the +4 and convert to a number or keep zip code values as strings.