first I would do a permission check in the ubb cp.
It should show all okay.
Now it does not check all folders and files. but it is a start.
Second I would double check:
Control Panel / Profile Settings[-] Avatars
Absolute PATH to Avatar Upload Storage Directory
But also make sure you click on the Test Directory link on the next line.
That writes a test file to that folder that is required.
It will provide a pass or fail popup if file permissions are okay or not.
To double check open your file manager and there should be a file like test.php in the correct folder.
Next double check:
Full URL To Avatar Upload Storage Directory
For this to be correct it would be the same path you use with a browser to view the image.
So if you say the file is on the site, Then you should be able to type the path in a browser to view it now.
Even if it does not show in the forum.
What ever that path is, that is what you use. don't forget the http and or www part of the url
The rest are sizes and should be okay as from what you say.
Select the update button and it should work.
Unless you have a cache issue that needs to be cleared.