Jürgen is right, the groups are the source of your problems.
There is an old saying in the theater: "Anyone who puts kids or animals on the stage deserves what happens to them." That means that no matter how well-behaved, or well-trained you think they are, at some time they are going to revert to their true nature, and you can only hope it doesn't happen during a performance. The SL correlation is: "Anyone who uses groups deserves what happens to them." That means that no matter how well-behaved or how well-trained you hope they are, groups don't play nicely with anything, and especially not states, clicking on, and triggers. Sooner or later, you are likely to have problems with them.
Groups don't work in SL. Take it from someone with lots of negative experiences, you can have groups, or you can have triggers and states that work, but not both.
Check the Without Group slide in the attached sample. If you like the way it works, here are the changes I made:
I selected the group of pictures, right-clicked, and exported them as an image.
I deleted the group, and inserted the picture from a file.
I ungrouped the next and prev images, and deleted the symbol. I clicked the rectangle, and typed the < and > symbols, resizing them to get what I wanted. (Selecting a shape and typing places that text on the shape, but as part of it, not as an additional object.)
Then I wrote a little note to tell the system where it was in the list of pictures. Programmer-type people call those notes variables.
You can read the triggers to see how I used the note to keep track of when to stop moving, and you already know how to create the motion paths.
Any questions, ask.
