According to the specs I looked up, the Ace comes with very little internal storage (158 MB). This internal storage is used for app installation as well as storage of a lot of app data like text messages. If you have a lot of apps installed, you might not have much room in internal storage for text messages. Also, if you have a lot of text message threads that you've been saving, that uses up storage as well (especially if they have photos or videos in them).
Can you post a screenshot of your storage screen (Settings/Storage)? If not, can you type out the numbers you see there?
If I'm right, then I would suggest uninstalling any app you really don't need, and deleting all saved text message threads.. Hopefully, that will clear up enough space for your text messages.