Microsoft have disabled WK4 and WK3 file types for Excel 2003 and Excel 2007. Annoying when you want to import them to a view. You can fix this by using this registry file.

You will see an error:

"You are attempting to save a file type that is blocked by your registry policy settings." when trying to save as.

Save this as Excel2003WK4.reg and then run it

Windows Registry Editor Version 5.00

[HKEY_CURRENT_USER\Software\Microsoft\Office\11.0\Excel\Security]

[HKEY_CURRENT_USER\Software\Microsoft\Office\11.0\Excel\Security\FileOpenBlock]
"BinaryFiles"=dword:00000000
"LotusandQuattroFiles"=dword:00000000

[HKEY_CURRENT_USER\Software\Microsoft\Office\11.0\Excel\Security\FileSaveBlock]
"BinaryFiles"=dword:00000000
"LotusandQuattroFiles"=dword:00000000

I think the same for 2007 would be:

Windows Registry Editor Version 5.00

[HKEY_CURRENT_USER\Software\Microsoft\Office\12.0\Excel\Security]

[HKEY_CURRENT_USER\Software\Microsoft\Office\12.0\Excel\Security\FileOpenBlock]
"BinaryFiles"=dword:00000000
"LotusandQuattroFiles"=dword:00000000

[HKEY_CURRENT_USER\Software\Microsoft\Office\12.0\Excel\Security\FileSaveBlock]
"BinaryFiles"=dword:00000000
"LotusandQuattroFiles"=dword:00000000

but I'm not sure.

NB I was a bit annoyed to find Symphony and Open Office do not support WK4 files. : (  

Thanks to Jez Greenwood for this.