When attempting to install application on your iPhone you might get a message stating that you are not able to install the application because you are not authorized on this computer. If you get this message and there is not another iTunes account configured for another iPhone on this computer then you need to authorize this computer for your iTunes account.
To authorize this computer click Store from the top menu and select Authorize computer from the drop down. Now sync the iTunes with your iPhone again and the application should install without issue.
Side Note:You are limited to authorize 5 computers per iTunes account.
If the above information does not resolve your issue click on this Apple Support link. Try the solutions available but the one that will probably work is the final solution regarding deleting the SC Info folder. Thanks to Alain4620 for providing the link in the comments below!