Why Does My Excel File Give an 'External Table is Not in the Expected Format' Error, and How Can I Fix It?

Troubleshooting Excel File Read Errors: "External table is not in the expected format"

This article addresses the common error "External table is not in the expected format" encountered when reading Excel 2007 (.xlsx) files. This error usually occurs when using outdated connection strings designed for older Excel versions.

Here's how to resolve this issue programmatically:

1. Update your connection string: Replace the obsolete "Microsoft.Jet.OLEDB.4.0" provider with the correct one for Excel 2007 and later:

<code class="language-csharp">public static string path = @"C:\src\RedirectApplication\RedirectApplication1s.xlsx";
public static string connStr = "Provider=Microsoft.ACE.OLEDB.12.0;Data Source=" + path + ";Extended Properties=Excel 12.0;";</code>

2. Verify the file path: Double-check that the path variable accurately points to your Excel file's location. Incorrect paths are a frequent source of this error.

3. Implement the corrected code: Use the updated connection string within your data access code:

<code class="language-csharp">using (OleDbDataAdapter adapter = new OleDbDataAdapter(sql, connStr)) {
    DataSet ds = new DataSet();
    adapter.Fill(ds);
}</code>

By following these steps, you can directly read your Excel 2007 files without encountering the "External table is not in the expected format" error, eliminating the need for manual pre-opening in Excel. Remember to install the appropriate Microsoft Access Database Engine if it's not already present on your system.

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