When working with search in SharePoint 2010 you might run into the error “The search request was unable to connect to the Search Service” in the Core Results webpart.
If or when this happens you should check a few things
Is the search service running?
Go to the server that handles search requests and select Start > Administrative tools > Services. Locate the service “SharePoint Server Search 14” and check that it is running
Is the Webapplication associated with the Search Server Service?
Go to Central administration > Manage Webapplications > click on the Webapplication that troubles you > Click Service Connection. In the windows “Configure Service Application associations” ensure that Search Service Application is checked
Have you altered the settings in the Search Core Results webpart?
Locate your Search Core results webpart > Edit Web Part > Location properties > select Location: none. If you might have selected “Local FAST search results” it wil result in the error “The search request was unable to connect to the Search Service” when FAST isn’t configured.
If none of these suggestions work and you might have found something else that could be causing this error please let me know.