Problems with syncing the first time

Hello everybody,

 I just started working with endnote a few days ago but already put a lot of work into it. Probably I was asked in the beginning to set up the syncing and missed it. And now I want to start using sync, but it does not work.

When checking my sync status I get this:

Sync Details
Sync was last run: Never
Sync Status: There are changes that need to be sent.
Error Code: Server.AuthenticationToken.invalidUserCredentials
Error Message: The username/password specified is not valid.

Local Sync Library
Library Name: My EndNote Library.enl
References: 259
Groups: 1
Group Sets: 1
Attachments: 19

Online Sync Library
Serial Number: Unable to contact the online service.
References: Unknown
Groups: Unknown
Group Sets: Unknown
Attachments: Unknown

Sync Limits
Number of References: Unknown
Number of Groups: Unknown
Number of Group Sets: Unknown
Attachment Storage: Unknown

What do I have to do now?

Thanks in advance