Now and again, but pretty infrequently, I cannot enter any data into a spreadsheet. It's as if the the workbook becomes locked or uneditable. The solution is simple, though; I just click on a cell in a different workbook, make a single keystroke and erase it, and then return to my original worksheet which is now editable or unlocked. Is this a bug in Excel or I am doing something I am not aware of to lock my spreadsheet? Thanks!