Hello,
it may be that the display profile property "searchserver" is not set to a valid Search server URL.
depending on the version of portal you are using the URL may be :
6.x : http://SERVER.DOMAIN:PORT/portal/search
7.x : http://SERVER.DOMAIN:PORT/mySearch/search
mySearch : being your search server instance
you may use the Desktop console to verify the value of the Discussions Channel.
hoping this helps