Do you have one of the calendar options selected under View-Today Pane?

No menu bar with View? Press the alt key.

The calendar options are grayed out in the view-today pane so can't select it.

Do you have a pane listing all your calendars down the left side of the main calendar window? If not select View-Calendar-Calendar List

If the list is not visible and but this option is checked in the menu, hover your mouse over the left margin of the window until it becomes a double headed arrow. Click and drag to the right to expose the list.

Right click your calendar, select Properties and make sure it is not marked Read Only

I am not sure this is it but since it states to select a writable calendar it is worth a shot.

I did all the things you said - found the list - the calendar was writable - was able to bring up the today pane in the calendar but not in email. then clicked a thick black arrow at the top of the today pane next to heading Events and Tasks. Then the pane mysteriously reappeared. Don't know what that arrow is for or why it brought back the pane. Thanks so much for your help.