This publication contains a table with a diagonal table cell. If this condition is not fixed and the publication is sent as an e-mail message, the text will be exported as an image when the publication is sent as an e-mail message. The image quality will be low, and the image will add to the file size of the e-mail message.
Note: To find and select the item, click the error message in the Design Checker task pane, click the arrow, and then click Go to this Item.
To fix the issue
You have to remove the diagonal from the table cell:
In 2016, 2013, and 2010 versions
Click on the table.
Under the Table Tools tab, click Layout.
In the Merge group, click Diagonals > No division.
In Publisher 2007
On the Table menu, click Cell Diagonals.
In the Cell Diagonals dialog box, click No division, and then click OK.