/why would data->sort be greyed out in Version: Build ID: (Version: Build ID: in a sheet with no graphics and no macros?

I have a smallish (smaller than 100 rows, 20 columns) with a mix of data and formulas. There are no macros or graphics. When I tried to sort some data (data → sort), the “sort” menu item was greyed out.

program: calc
Build ID:
uname -a gives me: Linux captain-ahab 3.17.8-300.fc21.x86_64 #1 SMP Thu Jan 8 23:32:49 UTC 2015 x86_64 x86_64 x86_64 GNU/Linux

Is the file set as read-only? There is an edit button next to the “email to” button that can be turned on/off. It’s possible the OS has set the file as read-only. If the file was opened through an email program, it may be set as read-only. The window title where the file name is shown, but have (read-only) in parenthesis. This occurs in Windows version.

Merged cells in the sort area may also disable sorting.