Cannot run MS Word app anymore using Microsoft.Office.Interop.Word in all of my VB.Net 4.8 programs

Question

Cannot run MS Word app anymore using Microsoft.Office.Interop.Word in all of my VB.Net 4.8 programs

Wolf Schubert 20

When running a Visual Studio 2022 test program with Imports Word = Microsoft.Office.Interop.Word I cannot run the program.

It fails with "Unhandled Exception: System.InvalidCastException: Unable to cast COM object of type 'Microsoft.Office.Interop.Word.ApplicationClass' to interface type 'Microsoft.Office.Interop.Word._Application'."

Source code:

Private Sub Button1_Click(sender As Object, e As EventArgs) Handles Button1.Click

    ' Date:     9/6/2025 WS

    Cursor = Cursors.WaitCursor

    Dim WordApp As New Word.Application

    Dim WordDoc As New Word.Document

    Try

        WordApp = GetObject(, "Word.Application")

        WordApp.Visible = True

        WordApp.ActiveDocument.Activate()

        WordApp.Documents.Open("TestDoc.docx")

    Catch ex As Exception

        lblErrorMsg.Text = ex.ToString

        Application.DoEvents()

    Finally

        WordApp.Quit(False)

        WordApp = Nothing

        System.GC.Collect()

        Cursor = Cursors.Default

    End Try

End Sub

This happens with all of my VS 2022 programs which were working fine previously.

VBNet_TestWordApp_1.jpg VBNet_TestWordApp_2.jpg VBNet_TestWordApp_3.jpg VBNet_TestWordApp_4.jpg VBNet_TestWordApp_5.jpg VBNet_TestWordApp_6.jpg VBNet_TestWordApp_7.jpg VBNet_TestWordApp_8.jpg VBNet_TestWordApp_9.jpg VBNet_TestWordApp_10.jpg VBNet_TestWordApp_Form1_1.jpg VBNet_TestWordApp_Form1_2.jpg VBNet_TestWordApp_Form1_3.jpg VBNet_TestWordApp_Form1_4.jpg

Viorel 124.9K Reputation points

2025-09-07T17:32:11.7666667+00:00

Try to remove this line: WordApp = GetObject(, "Word.Application").

Answer accepted by question author

2 additional answers

Your answer

Viorel 124.9K Reputation points

2025-09-07T17:32:11.7666667+00:00

Try to remove this line: WordApp = GetObject(, "Word.Application").

Answer 1

Thank you for sharing details.

Why This Happens

When your VB.NET application automates Microsoft Word, it communicates through a COM proxy. Your project is compiled against an interop assembly (Microsoft.Office.Interop.Word) that defines the interfaces and methods expected at runtime.

This error occurs when the COM proxy Word provides doesn’t match the interop type your app expects. Common causes include:

Bitness mismatch
Word is installed as 32-bit but your app runs as 64-bit (or vice versa). A 32-bit Office cannot be automated from a 64-bit process.

Interop version or embedding differences
Your project may use embedded interop types or a different version of the PIA than the installed Office.

Broken COM registration
Office updates or Click-to-Run installations can alter or break registry entries for Word’s COM classes.

Conflicting assemblies
Multiple versions of the interop DLLs in the GAC or your project can confuse .NET into binding to the wrong one.

Because .NET expects an exact match to _Application, any of these issues can cause a System.InvalidCastException.

Recommended Fixes (Try in This Order)

Match Word Bitness with Your Project

Open Word → File → Account → About Word → check if it’s 32-bit or 64-bit.
In Visual Studio → Project Properties → Build → Platform Target → set to x86 (for 32-bit Word) or x64 (for 64-bit Word).
Avoid “Any CPU.”
Configure projects to target platforms

Check the Interop Reference Settings

In Solution Explorer → select Microsoft.Office.Interop.Word.
In Properties → set Embed Interop Types = False.
This ensures your app uses the installed PIA instead of embedded stubs.
Office primary interop assemblies

Repair Microsoft Office

Go to Control Panel → Programs → Programs and Features.
Select Microsoft Office → Change → choose Quick Repair (and Online Repair if needed).
Repair an Office application

Re-add the Interop Reference

Remove the current Microsoft.Office.Interop.Word reference.
Re-add it manually or install the official NuGet package for a clean version.
Microsoft.Office.Interop.Word NuGet package

Consider Alternatives for Server or Background Use

Microsoft does not recommend automating Office in unattended or server environments. For these cases, consider:

Summary

In most cases, correcting the Platform Target and setting Embed Interop Types = False resolves the error. If not, repairing Office and re-adding the reference usually helps.

If You Still See the Error

Please share the following details:

The version of Microsoft Office (32-bit or 64-bit).
Your Visual Studio Project’s Platform Target setting.
The Embed Interop Types property value for the Word reference.
Whether you’ve already tried an Office repair or reinstall.

This information will make it much easier to pinpoint the cause and suggest the next step.

Let me know if you need any further help with this. We'll be happy to assist.

If you find this helpful, please mark this as answered.

Answer 2

Wolf Schubert 20

I tried that and the result is the same.

Even when I comment out the following 2:

        ''WordApp = GetObject(, "Word.Application")

        ''WordApp.Visible = True

        ''WordApp.ActiveDocument.Activate()

        WordApp.Documents.Open("TestDoc.docx")

    Catch ex As Exception

        lblErrorMsg.Text = ex.ToString

        Application.DoEvents()

I still get this failure when executing the last one (WordApp.Documents.Open("TestDoc.docx").

Answer 3

Wolf Schubert 20

This response was one of the best I've ever seen. Thank you.

The problem was, it turns out, your

"Bitness mismatch Word is installed as 32-bit but your app runs as 64-bit (or vice versa). A 32-bit Office cannot be automated from a 64-bit process."

Office 32bit was running on a Windows 64bit system.

My application compiles and runs now perfectly under Office Pro 64bit and Windows 11 24H2 64bit.

I also had to move the "WordApp.ActiveDocument.Activate()" statement after the Open statement.

WordApp = GetObject(, "Word.Application")

WordApp.Visible = True

WordApp.Documents.Open("TestDoc.docx")

WordApp.ActiveDocument.Activate()

(I switched from Windows 10 to Windows 11 also.)

Thank you for your fast response. Breathing fresh air now. :-)

Varsha Dundigalla(INFOSYS LIMITED) 2,785 Reputation points Microsoft External Staff

2025-09-09T09:26:15.2766667+00:00

Thank you for the update it's good to hear that everything is working smoothly now with Office Pro 64-bit and Windows 11!

Really appreciate you sharing the details, especially about the WordApp.ActiveDocument.Activate() adjustment and the bitness mismatch. It’s great to know the switch resolved the issue and your application is running perfectly.

As you've confirmed the resolution, we'll go ahead and consider this case closed. If you ever run into any further issues, please feel free to raise a new thread. We’re happy to assist.

Share via

Cannot run MS Word app anymore using Microsoft.Office.Interop.Word in all of my VB.Net 4.8 programs

2 additional answers

Your answer