I have a valid 24 word mnemonic string for a GreenAddress wallet, but I can't log in. I enter the mnemonics, it decodes up to 100%, then it offers me to add a 4-digit PIN, I enter 4 digits and hit Confirm, but then it just stays there.

The words seem valid (if I deliberately omit or mistype one, just to test, it says "Invalid mnemonic: Checksum does not match").

Tried Chrome as well as Firefox, on both Mac OS X and Windows, using fresh clean browser or private window (to get rid of any earlier cookies) but no go.

What should I do?