Jon and Joe -
Thanks for the replies, especially the screen shot.
Not sure what was going on yesterday. I just opened a new project and the Frame Rate drop down shows up (as in your screen shot).
Then re-opened the project I was working on yesterday and that works fine too.
Only thing I can think of is that the way I had my windows sized, my Basic Video Settings in the video tab must have cut off above the frame rate dropdown and I didn't notice the scroll bar to the right, indicating more content in that window.
Thanks again for the help. I'd worked around things yesterday by creating a new sequence and giving it the required properties from the start, but was worried this would be a recurring problem.