Issue with Smartsheet Cell Limit - Data Shuttle

I'm trying to use Data Shuttle to import data into a Sheet upon attachment of an Excel workbook to the same sheet.

When I attempt to run this Data Shuttle, I am getting an error that I have exceeded the 500,000 cell limit.

The parameters of my source Excel sheet are as follows:

Cells: 401,668

Columns: 40

Rows: 10,280

I have not exceeded any limits according to this: System requirements and guidelines for using Smartsheet | Smartsheet Learning Center

Can someone help me troubleshoot this issue?