Following the guide for changing the content of a worksheet cell here http://code.google.com/apis/spreadsheets/data/3.0/developers_guide.html#UpdatingCells I kept getting "HTTP Error 403: Forbidden"
After a lot of head-scratching I found out that the section about the HTTP If-Match header that is included e.g. here: http://code.google.com/apis/spreadsheets/data/3.0/developers_guide.html#UpdatingListRows applies to changing the content of cells too, but is missing from the documentation about how to update a cell. Without the If-Match header changing the cell is not allowed. Please update the documentation!
