According to rorya's advice, please try the following:-
"Check under Excel Options, in the Advanced section, there is a setting called something like 'Ignore other applications using Dynamic Data Exchange (DDE)' - make sure this option is not checked."
Source:
http://www.experts-exchange.com/Software/Office_Productivity/Office_Suites/MS_Office/Excel/Q_23319730.html?sfQueryTermInfo=1+cannot+desktop+from+open+vista+xl