When doing Mail Merge (Word and Excel), I received this error Error has occurred: "Sheet 1$" is not a valid name. Make sure that it does not include invalid characters or punctuation and that it is not too long.

This is the solution that worked for me: recreate the connection.
- Click OK on "Sheet 1$" error box.
- Click on Find Data Source... button.

- Double-click on +Connect to New Data Source.odc
- Select ODBC DSN

- Select Excel Files

- Browse for Excel file where your list of clients/data are entered. Then click OK.

- Select the table/sheet name.

- Click Finish to save data connection file.

- Microsoft Word will open. Go to Mailings menu, then preview individual result by clicking the arrow.

- Save the Word document.