Redirect website with htaccess

RewriteEngine on
RewriteRule (.+) http://newdomain.com/$1 [R=301,L]

I am using Wordpress and this is my htaccess configuration file, everything seems to be working except this one. This URL:

http://olddomain.com/wp-content/uploads/2012/12/abc-1-th开发者_开发技巧umb.jpg

Redirects to:

http://newdomain.com/403.shtml

Instead of:

http://newdomain.com/wp-content/uploads/2012/12/abc-1-thumb.jpg

Examples:

http://mister-gan.com/wp-content/uploads/2011/02/simple-and-clean-2.png
http://ganchinhock.com/wp-content/uploads/2011/02/simple-and-clean-2.png

May I know why?

RewriteEngine on
RewriteRule (.+) http://newdomain.com/$1 [R=301,L]
Redirect 301 http://olddomain.com/wp-content/uploads/2012/12/abc-1-thumb.jpg http://newdomain.com/403.shtml

Upon @Wige's comment and rephrasing your question it seems that there is a permissions problem in one of the subdirectories on the new domain, as 403 is a permissions error.