Can't save as bitmap

This happens regularly. I work on something and when it's ready, I "convert to Bitmap". When it's converted I go to the "right click menu" (sorry, I've been abroad too long and can't remember the english word I need).  But unfortunately the "save bitmap as. . ." is greyed out. I can't think of a workaround (tried copying to a brand new document but that didn't work.)

I've been doing this for YEARS and every once in a while this happens. Anybody have an idea?