This results from your spreadsheet software automatically recognizing the UPCs as a long number. Thus, it saves it in scientific notation.

Example: 12345678901 shows as 1.23E+10

To fix this, you can either:

   1. Select the cells with scientific notation, right-click->Format Cells->Select Text and click “OK”

 

   2. You can also highlight the UPC column, and then select “General” from the format box dropdown on the “Home” tab of Excel:

 

Here are some additional articles you may find useful:

UPCs for Handmade Products
Saving & Validating UPCs