This can occur if you have used the Project Manager option to move the file to your Excel Startup folder. To resolve the issue, start Excel and let the Project Manager file open. If it is hidden, select Unhide from the Project menu at the top of the Excel window. Then from the Project menu select Options and click the button that says "Remove Project Manager from the Excel Startup Folder". This will automatically move the file to your Excel default folder and it will no longer open when you start Excel. If you no longer want to use the file, you can delete it from your Excel default folder which is usually the My Documents or Documents folder.
The Project Manager for Excel workbook is fully protected to prevent accidental changes to outline or worksheet structure that would keep the program from functioning properly. However, the program is designed to give you all the functionality you need without unprotecting it. To edit a task or project just double-click on it or use the Edit button. Just search the help file for the task you want to perform and there should be a program function that will suit your needs.
This problem occurs in Excel 2007 when the file you are importing from and the file you are importing to are saved in different file formats. If you are importing into a file saved in the new Excel 2007 file format (.xlsm) then be sure to open the old file separately and save it into the new Excel 2007 file format (.xlsm) before importing it into the new version. You can also save both files in the Excel 97-2003 format (.xls) first and then import the data from the old file into the new version. As long as both files are in the same format the outline structure will be maintained during the import process.