Here's a step by step procedure to create the problem.
Put a still picture on the video track.
Double click on the still picture to open the 'pan and zoom' window.
Put a checkmark in 'start to finish'.
Set an end value.
Close.
Click on the 'T' to open the title overlay window.
The 'title overlay' window will open and imediately switch back to the 'pan from start to finish' window.
You have to remove the 'pan and zoom' before you can do the title overlay.
There are some other work arounds, but this demonstrates the problem.
Don