While working with SharePoint, I got an error in search service when I try to index a page having search results using for roll the content in site collection. My search service application and content source are working fine. After checking this error in logs and digging in to this error I found that we have to change User agent value.
To do that,
Open Registry editor (Run -> regedit) and navigate to “HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Office Server\14.0\Search\Global\Gathering Manager” key.
Change the value of “User Agent” from “MSIE 4.01” to “MSIS 8.0” and restart SharePoint search service.