unable to cast COM object of type 'microsoft.Office.Interop.Excel.ApplicationClass' to 'microsoft.Office.Interop.Excel.Application'"

If this is not a code related error than please remove below given key from registry.

Steps:

Start--> Run --> regedit --> HKEY_CLASSES_ROOT-->TypeLib-->{00020813-0000-0000-C000-000000000046} --> 1.8/1.7 (Delete this)

Solution: This issue can be resolved by deleting an invalid registry key left over from the higher version of Office. Follow the above steps.

Cause: This issue is caused by a left over registry key if you have downgraded your version of Microsoft Office from either Office 2010 to Office 2007, or Office 2013 to Office 2010 or 2007.

Let me know if this solution is not helped to you

Microsoft Office 365

I was running Microsoft Office 365 with Windows 10 and tried the mentioned solutions to remove the registry key without success.

I went to the control panel in an attempt to repair the Office 365 suite.

1. Right Click on Start Menu
2. Click Apps and Features
3. Search Microsoft 365
4. Click Microsoft 365
5. Click Modify

I selected the quick repair

Tried my program again and everything worked!

I am sure the answers to this question (and similar questions) proposing editing the registry and removing old references to versions of Office no longer on the machine are correct.

I am only adding this answer because I am currently kicking myself. Two hours spent hunting keys in the registry and getting nowhere. Last throw of the dice was to try a simple repair on Microsoft Office and suddenly my error is gone.

... seems to me it's worth trying a repair before getting too deep into manually editing the registry.