Solved Excel sheet will not open after server restart

Excel sheets that were open when the server shut down will now not open. I get the following error message: "The file your are trying to open, report.xls, is in a different format than specified by the file extension. Verify tat the file is not corrupted and is from a trusted source before opening the file. Do you want to open the file now?" Yes No Help If i push ctrl+shift+I i get the code: 101786