Links updating problem after upgrading Excel 2000 to Excel 2002

I support an end user whose spreadsheet links are taking "forever" now that I have upgraded her to Excel 2002. On Excel 2000 they executed quickly. I've checked the links, and they seem to be correct. However, I do notice that some are using mapped drive letters to our server while others are using the UNC. I don't know if that makes any difference. I changed them all to the same format, but they revert back to their former formats. When I queried the end user further, she said some days the links update in a satisfactory time window, other days not. Since this was never a problem with Excel 2000, I'm not sure that I can blame this on the network. Any ideas out there ?