Index: branches/5.1.x/core/admin_templates/js/uploader/upload_manager.js
===================================================================
diff -u -N -r13659 -r13667
--- branches/5.1.x/core/admin_templates/js/uploader/upload_manager.js	(.../upload_manager.js)	(revision 13659)
+++ branches/5.1.x/core/admin_templates/js/uploader/upload_manager.js	(.../upload_manager.js)	(revision 13667)
@@ -118,7 +118,7 @@
 	var $uploader = this._Uploaders[uploader_id];
 
 	Request.makeRequest(
-		$uploader.deleteURL.replace('#FILE#', fname).replace('#FIELD#', $uploader.params.field),
+		$uploader.deleteURL.replace('#FILE#', encodeURIComponent(fname)).replace('#FIELD#', $uploader.params.field),
 		false, '',
 		function(req, fname, $uploader) {
 			$uploader.removeFile({id:fname})