Old stuff ain’t safe. At least according to Microsoft. Therefore, when you try to open files in the 97-2003 file format (or earlier), Office 2010 will block editing (and macros) of these files until you decide they are safe. The problem arises when you upgrade, all your files are in the previous format and blocked from editing. You can easily click the Enable Editing button that appears in the yellow bar under the ribbon, but if you want to be proactive, you can change this setting.
In Word or Excel, go to the File tab, click Options, click Trust Center on the left, and then click the Trust Center Settings.. button. On the left, select File Block Settings, and remove the checkmarks from the older Office files that you want Office 2010 to open. There are additional settings for how to open at the bottom of the dialog box.