Excel File is Locked for Editing

I recently built a VB.NET project which reads some data from text files and then populates an Excel spreadsheet. In this sheet there are some formulas which I use to build some bar charts. The boss liked this so well he did some kind of link to it from another file to post it on a big screen TV in the customer service room. Since he did this my program can no longer write to this Excel file. Each time I try it is throws an exception indicating that the file is locked. Even when I just try to open the file it pops ups a window which says the file is locked for editing by 'User'. There is no one using that login name as far as I know on this network. And of course the boss says I'm crazy and he's not acknowledging that the link he created could be causing the trouble. To test my theory, I built another Excel file in the same folder and I can write to it via my program all I want. But when I try to go back to the original file. it fails.

Can anyone comment on this?