LO 3.5 calc/.xls file problems

Win 7, 64bit OS. LO 3.5 doesn’t allow adding new sheets nor renaming an existing sheet in an excel file. Why/ how can I do this? The options are greyed out.
Opening a new spreadsheet in LO 3.5 allows both of the above, however.

Where you get the xls?, if it is an email attached file, you need to put in edit mode.
Two ways, save the attached file in a directory with read/write access and open it from LibreOffice, or open from attached and change to edit mode with the button just over/left Export to pdf.