Can not add transitions to my project

I have almost finished a project in Final Cut Pro 10.1.1 and exchanged som still images of the same length.
Now I can not add transitions. I get the message: There is not enough extra media beyond clip edges to create the transition. When i press the " create transition" nothing happens.
I can't see that there shouldn't be enough media...Everything looks normal.
Tankful for any help on this topic!

When you replaced the clips you have created a situation where there is no "handle". If you click on the leading edge of the clip you will get a red highlight. That means it is the very beginning (time-wise) of the file. Select the trim tool (T), click and hold in the middle of the clip. Drag to the left. You will see a little window open up that tells you how much you are dragging. It will indicate something like -00:15. That is the time in seconds and frames that you are "slipping" the clip. Keep dragging to the left until you have gone a second or so. You will then be able to add transitions. If you change the timeline clip appearance to one that shows thumbnails you will get a better idea visually of what is happening.

Thank's a lot. Problem solved! You just made my day.

With only one image left, I can only get the transition to the left, not on the right side....
Have tried to drag the trim tool, with out any luck...

What type of file is it?

It's a jpg file 1600 X 1063.

If you click on the right edge do you get a red or yellow highlight? Is it inside a compound clip? You shouldn't have any problem on the right end with a jpg. It the jpg transitioning to something else or just fading out? If it's transitioning to footage, for example, you have to make sure the footage is not at the beginning of the file. In other words if you click on it's left edge is it highlighted in red or yellow. If red then follow the same procedure.

I get a yellow highlight when i click on the right edge?
It's not a compound clip and the jpg is transitioning to another jpg file and the left edge is yellow....