Problem with macros in Excel 2000

I developed an Excel 2003 spreadsheet with an embedded worksheet form button with an assigned macro written in VBA. The Excel file is hosted on a web server. User will open the Excel file from a web page via IE browser.

After deploying, we got some issues from users that it throws the below error.
"The macro cannot be found."

where is the correct & complete path of the assigned macro.

It seems to me that the macros perhaps somehow "disappeared" when users open in Excel 2000 in web browser. I have tried the following but doesn't help:

- Set macro security to LOW
- Reprogrammed embedded worksheet form button to point to the full complete macro path
- Clear browser cache

What else to check? Any advice would be appreciated.