User blog comment:Carrie365/Help on Mod Installation!/@comment-4674838-20120313225942

If you bought Terraria on Steam, it should be in the steamapps folder. You can always go to your games library on Steam, select Terraria and choose "Delete Local Content," and then redownload the game through Steam for free. That will give you a 100% fresh install to your steamapps folder.

It sounds to me like you're encountering an error message that you're not supposed to be getting. I suggest taking a screenshot, uploading it to say http://tinypic.com/ and then posting the link in your blog here. Also, you'll need to state the name of the mod you're playing (there's lots of different mods), and you should probably say which Operating System you're using (e.g. Windows 7).

^This kind of information will help people to help you. Your current blog post is pretty vague.