SIMILAR IMAGE(S) ALREADY SUBMITTED

There are 3 different possibilities:

• your images are indeed similar.
• you are submitting a crowded theme and the moderator decided that your assets do not have enough outstanding.
• the moderator wanted to refuse the asset, but selected the wrong topic. 

If you have pictures of a dog playing with a ball, and that is your title, but the pictures are distinct enough, than the are OK. You can use the same title, even that this makes finding your asset less probable. Variations of the title give your pictures a higher chance that one of those get displayed by the search engine.

Similar images could mean that they are "similar" to other images that you have submitted or that there are too many "similar" images already available in the entire database.

As far as the tiles go. I myself, have several images with similar titles and have never had a problem. It is however, not a good idea because the title is used when buyers search for images. It could also be considered spamming which could result in your account being suspended.