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