I've seen this one several times. Clearing Chrome's cache or even reinstalling it won't help. Changing Chrome channel (stable, beta, dev) or won't help as well. It's definitely a Web Clipper bug. My guess is that during sign in process Web Clipper checks for some string in the registry (probably made by desktop Evernote client), that is somehow unreadable or incompatible with it. Did you install Web Clipper after installing desktop Evernote client? If so, then you may want to try uninstalling desktop version and see if it helps.