Is it 200 x 200 or less? That's important.

Maybe the link is off google and it's 400 characters long?
I use Imgur.com
Just upload the file and it'll give u a nice and easy link to copy/paste onto the site.
There are a 100 other sites that do the same thing too.
If that doesnt work then try showing us some screenshots. This is actually very easy to resolve lol.

Btw, you're posting in the wrong section. Off-topic or technical support would have been correct.

Very simple

Search in google- "ur desired picture type" 200 x 200 images
copy image address from there
then open BD forums and go to user control panel

and paste it in avatar
and then click submit