Try this. This is just a way of illustrating enzo’s point.
Create two titles,
Cut the first one into the timeline.
With the second one, mark an in at the front of the clip in the viewer and an out at the ten second mark. Cut it in as the next event in the timeline.
When you try to put a dissolve between them you will find that there is not enough media to do the trnasition.
This is Final CUts very polite way of telling you you have asked it to do something it can not do. You need to trim the shot by half the dissolve amount. IE; 30 frame dissolve you need to trim you shot by 15 frames because half of teh dissolve happens on one shot and half on the other.
David