i had this problem as well, i found a way to fix it
you can remove items from the chest Avast stores programs it deems threats in. open avast, and go to statistics.
after that, go to component stats. you should see a listing that opens your chest, and you can restore it. right click the terraria executable, and then select "restore".
finally, if you have the game on steam, right click it in your library's listing. go to properties, and then to the "local files" tab. verify the integrity of the game cache, and it should work.