Searching the Web of Knowledge (WoK) / Web of Science directly from within Reference Manager or EndNote is only possible if the IP address of your computer has been authenticated.  A list of institutions with IP access on campus can be found at: http://wok.mimas.ac.uk/full_subscribers.html.  

"Any direct search option ie searching using the search form of bibliographic software will require IP access, if you need to use an Athens username and password to login to the service this direct search option will not work. A list of institutions with IP access on campus can be found at: http://wok.mimas.ac.uk/full_subscribers.html Unfortunately it is not possible to enable IP access for individual users."

If your institution is not listed, or you are wanting to use the Web of Knowledge from an machine that is not IP authenticated (e.g home machine), then using an Athens username and password to login from within Reference Manager or EndNote will not work.  Please log into the Web of Knowledge using an Internet browser and use the Direct Export option having found your references.