A table row was X columns wide, which is less than the column count established by the first row (Y).

A <table> contains a <tr> row that has less <td> columns than the column count established by the first row. Check the table to ensure all rows have the same number of columns.

For example, in the following table, the first <tr> row defines that it’s 2 columns wide, but the second <tr> row tries to use only 1 column:

<table>
<!-- This first row sets the table as 2 columns wide -->

  <tr>
    <td>First</td>
    <td>Second</td>
  </tr>

<!-- This second row has only 1 column -->

  <tr>
    <td>Wrong</td>
  </tr>
</table>

Learn more:

MDN Reference

MDN: The table element

→

WHATWG Spec

HTML Spec: The table element

→