Excel Security Warning Notice for hyperlinks. HELP!

Hello,

I have an ongoing problem with Excel2010 when i insert hyperlinks onto a spreadsheet. The link will work for a few days and then stop working, meaning i have to manually find the files on my network (which is very annoying!). When the links stop working, a security warning pops up (see attachment to see this). Does anybody know how to stop this happeneing and making the links work forever?

Any help would be much appreciated,
Thanks!