Excel sheet opening as read only in 2010

Please bear with me as I explain the problem.

I have a large spreadsheet with macros written in Excel 2007 on a networked PC in our office. Two other networked PCs running 2007 can open the file and macros work fine, it opens in normal mode and any changes can be saved.

IT have now supplied a new PC with Excel 2010 installed for new member of staff. On this new PC I can now access the file and open it and the macros will run EXCEPT it opens in EDIT mode only. I have tried all options I can find but can not get the file to open in normal mode.

My guess is that it is something to do with the extra security Microsoft has added in to 2010 and they seem to have broken a perfectly good system.

Can anyone suggest, apart from uninstalling 2010 and installing 2007, a way to make this work properly?

Many thanks

No, the file opens OK for three PC's, the one it is one and the the two that access it across the network, These all run 2007 not 2010. It is only in version 2010 that it opens as Read Only