Are you using the same account (and keyfile) to login as before? Can you right-click -> Manage Permissions and check the permissions?
If it does not resolve your problem, you could create a debug log and send it to us so that we can analyze what's wrong. A debug log contains detailed information about what happens within Boxcryptor so that we are able investigate your issue.
You can find instructions on how to create a debug log by following this link:
Please note that the debug log may contain sensitive information (e.g. filenames) - however, it will never contain file content. Please send the report to firstname.lastname@example.org.