To confirm, you have the primary key set as products_id and have it entered in the User defined products field?

here is my configuration
Title Value Action Uploads Directory EPtemp/
Uploads Directory Admin/Catalog true Info
Import/Export Primary Key products_id Info
Upload File Date Format m-d-y Info
Default Raw Time 09:00:00 Info
Upload/Download Prices Include Tax false Info
Verbose Feedback true Info
Show all EP4 Filetypes with Files true Info
Replace Blank Image false Info
Make Zero Qty Products Inactive false Info
Smart Tags Replacement of Newlines true Info
Advanced Smart Tags false Info
Debug Logging true Info
Maximum Quantity Discounts 3 Info
Split On Number of Records 2000 Info
Script Execution Time 60 Info
Convert Curly Quotes, etc. 0 Info
Convert Character 0x92 1 Info
Enable Products Meta Data 1 Info
Enable Products Music Data 0 Info
User Defined Products Fields products_id Info
Export URI with Prod and or Cat 0