Same problem for me. I registered for a free account from my private laptop. Now I want to share the data on my company pc. However, that lives behind a proxy. The proxy is configures in IE, but that doesn't help.
I've tried to create a local account on the company pc, using the same user and password. I can then see the encrypted files on Dropbox in green. However, I cannot open them.
So, I tried to convert this local account to a Boxcryptor account (Settings -> Account -> "Change your account details" or "Convert to Boxcryptor account". However, both just open some boxcryptor web pages in the browser.
No clue how to proceed from here.