Can you help with EXCEL found unreadable content?

I copied and pasted data from Excel 2010 to Excel 2007, the formulas are simple and I used some colours to highlight certain cells and then I saved the document and exited. But when I want to open the file again I get the message Excel found unreadable content. When I click yes it removes all text formating and I lose all the colours I need to group important cells. Do you have a solution?