You deleted everything from your USB key or a drive, so there should be enough free space to copy the new files, but you still get the not enough free space message in Mac OS X? This is what you need to do.
Many times I find myself with a large number of opened tabs in Firefox browsers and thankfully you don't need to close the program in order to close all the tabs except the one I want to keep.
When you want to copy the result of the cell to another cell in Excel, the target displays an invalid references error messag. This error can be avoided by copying cell value into target cell and not the whole formulas.