Excel 2007 Hyperlink error

I have created Hyperlinks from an Excel 2007 spreadsheet to Word and PDF files in other drives on a shared network. The links work initially. When the file is saved (also on the network) however, the link no longer works.

The address used for the link has changed from L:\Certified Fisheries\Cornish sardine to
..\..\Fisheries\Certified%20Fisheries\Cornish%20sardine

The error message reads: The address of this site is not valid. Check the address and try again.

I found some solutions on the internet to similar problems which involved changing the hyperlink base (File|Properties|Summary Tab|Hyperlink Base). I can't figure out how to do this in Excel 2007 and therefore can't tell if it will work.

Any ideas?