If you are having trouble logging into 480px you may try this. Unlink your Facebook account from your 500px.com account. There are some Facebook IDs that cause a problem with 480px. This will be fixed in the next update coming soon.
If you need the accounts linked because you use Facebook to log in to 500px, then please just be patient and wait for the update to become available in the store. Keep your eyes on this space for announcements…
p.s. If you want the gory details, check if your Facebook ID is less than 2,000,000,000 or so (if it fits into a signed int, for your programmers out there), then you should be able to log in. Many people have something like 100000xxxxxxxxx which is causing the issue.
UPDATE: fixed version was submitted to the store on 1/23
Negative Eddy 
Will there be an option to login with a Twitter account?
Thanks for working on this awesome app Eddy! However, I noticed that I could not login using my Twitter account; FB was the only option. Could you please take a look at that? Thanks!
That login page is controlled by 500px. I’m not sure why they dont have twitter on it. I’ll send them a note and see if they plan to update it anytime soon.
I am sure you are right…however it is strange to offer the option to login using a Twitter account from the login page and then provide access to mobile apps via a page where Twitter accounts are not an option for logging in… if I only knew that earlier I would have created an account using an alternative method.
Thank you for looking into this!