Cannot load external image with special characters in file name

I’ve made an application which loads external images using URLRequest and URLLoader. Everything works fine until it needs to load an image which has special characters in the file name/location, e.g. ‘ú’ or ‘ð’, and then it doesn’t load anything.

when i run the .swf file locally it works, but if i run it when it’s embedded on an html page, it doesn’t work.

Does anybody know how to get around this? Many thanks in advance!