Maybe elements is limited to adding 2 titles? (Just kidding) That's not supposed to happen. A way to work around that (I works in pro, not so sure about elements) is when you have a title in the timeline to double click on it and the title dialog screen opens, change the title text to something else and (important) select "file" - "save as" and give it a new name in the save dialog box that pops up. Then you will see that the newly saved title has appeared in you projects screen and you can drag in onto the time line. Remember it's important to select save as, if you don't you will just overwrite the original one with the changes which is not the intention.
For the error that appeared, closing elements and starting it up again might help also, although adobe delivers very stable software sometimes it can act weird.