I don’t know if this is of any use to you, but it was because our hosting providing blocks .aspx and .asp by default on the shared linux platform. it was fixed by adding the following to .htaccess:
<FilesMatch “(?i)\.aspx$”>
allow from all
</FilesMatch>
<FilesMatch “(?i)\.asp$”>
allow from all
</FilesMatch>
After that the plugin can redirect all links