Are you getting this error message on Ubuntu 11.10 when trying to open .xlsx files by double-clicking?
Dragging the said file to Launcher where Calc sits, the file is opened without a problem. Opening it from LibreOffice itself is not a problem too. So why do you get an error when you double-click the file from Nautilus?
Thankfully the error shows some kind of hint. It says archive when it is supposed to be a MS Office 2007/2010 XML document. Ahhh… it looks like the default application for this file type is set to the wrong application. Right-clicking on the file tells us that Archive Manager has dibs on the file.
To correct this, right-click on the .xlsx file then choose Properties. Select the Open With tab. Proceed by highlighting LibreOffice in the list then click on Set As Default. Now you’re set. Double-click on the .xlsx file again and it should now correctly open with LibreOffice. You only need to do this once. All .xlsx files will now open with LibreOffice.
Note: It looks like the same error is encountered when opening a .docx file. Repeat the steps above but this time on a .docx file.