You might already be aware that the text message Error 34 and 107 when trying to send text messages was supposed to be corrected in software version LN510ZVB which is the one prior to your current one. Try deleting your cookies and cache by going to Main Menu from your home screen, go to Settings, Reset/Delete, enter your lock code (if not set up use last 4 of your telephone number), select Delete Stuff and touch Browser Cookies and Cache. If you would private message me, I will be glad to reprovision your text messaging to see if this also helps.
Sprint Tech Support
Sprint S.M.A.R.T Agents Sprint S.M.A.R.T Agent are here to help Monday through Friday 6:00 AM CT - 6:00 PM CT. If you need to speak to an agent outside of these hours, please visit Sprint Chat