This can happen for many reasons, the error itself is self explanatory. One or more assets in the game corrupts. I suggest saving the place to your files and uploading it again.
Error 403 means a bad request. In this case, it is because the image has either been modedrated or put offsale. It’s nothing to worry about, it means one of his plugin icons or images has been deleted.
Edit: HA HA, NOOBS, I HAVE TWO SOLUTIONS ON THE DEV FOURM NOW!!