Compatibility Issue with going form 07 excel to 2010 excel

I created a workbook to help track my daily activities along with my clients to help figure out my target market. I showed a few people around the office and they wanted to start using it. A few people can not use it and the difference is, is that they are using Excel 2010. Attached is the file if someone could let me know if there is something on my end I can do(save it differently?) to make it more compatible for the 2010 user. Or is there something they can do to make there excel compatible with the 07 version.

Basically the problem was is we would try and open it on the 2010 version of the software and it wouldn't open and it gave a compatibility error.

Thanks for the help in advance.

I forgot to mention I saved it as a binary excel because i thought it would save as a smaller file size. But the file we have tried was xlsx

any other suggestions?