Import/Export Tool 2.26 - Worked, then stopped? HELP!

Using OC 2.0.1.1 with Import/Export Tool v.2.26 - JNeuhoff

I have vqmod installed (I know this ext doesn't need it)

This ext seems to have a mind of own. I spent most of today trying to get it to import, adding single products or just importing unchanged files, sometimes it worked, other times it didn't.

Finally, I just wiped all demo products/categories off and manually added my categories and a few of my own products. Exported products to Excel, added a few products by cut/paste from my old product sheet. Imported back to OC, Voila! Worked fine.

Carried on the same method, adding by categories (very small number of items - only in the tens). The last add did not work, I get this error on the Import/Export page:

Uploaded spreadsheet file has validation errors!

The error log reads:

2015-06-24 19:51:21 - Export/Import: Missing product_ids in worksheet 'Products'!

I did everything exactly the same as when it worked, checked spreadsheet formatting, checked product_id numbers. I have no product options etc.

I have no idea what is wrong. Please help JNeuhoff or anyone who might know what's going on. Appreciate your time!

This happened to me and it just ended up being cells with null data somewhere in the product_id column.

Selecting several of the empty ones and deleting them solved the issue for me.