Dimsumgurl, each product when sent to be imported must be assigned to a category, otherwise where would it show up in the store? So to do that, a product is expected to have a category assigned to it. Further, if the category assigned doesn't exist (yet) then it is to be created. Thing with a category is that like a product with attributes, a category has several other characteristics. Those characteristics are/can be assigned separately from the product creation.

You mention that there was no categories_description field, in the import file, which is expectedly true, but was a v_category_name_X field present and populated with something? Where X represents the language number seen on the EP4 tools page on the right side?

It sounds like as the error message eludes, that a new category was generated, but the new category_description could not be assigned because the database is expecting either a value to be provided or a default value on the field.