Captivate 2 Cannot add or edit caption boxes

All was going good on my training program and I am up to around 570 slides with more to go. I cannot add a caption or edit any exist caption. Nothing is locked. I can open different slides but cannot add anything or edit anything. I have tried double clicking the caption box and in the timeline, right mouse click to menu and using the toolbar menu and nothing works. I can preview and all works fine in the presentation but I am not finished with the project. I have saved as another file and eliminated the last slides I created and still nothing. I thought about reloading Captivate 2 but I checked other projects I had done and I can add and edit captions on them. What happened and what can I do to fix this? Is there a file size limit? Help!!