Cannot open password-protected Excel File
 

I have an Excel file I've used for years. I had created this file with Excel
2003 on Windows XP Professional. The file was encrypted and password
protected.
I have recently upgraded to Windows Vista Home Basic and re-loaded Office
2003 and upgraded to SP3. However, I cannot open this Excel file, though I
know the password.
I keep getting the following error:
"Excel cannot open this file. The encryption type used is not available,
contact the author of the file. More encryption types are available using the
High Encryption Pack."

Any help would be appreciated.