You use the Microsoft Search service (Mssearch.exe) to perform a crawl for many documents in Microsoft SharePoint Server 2010. Then, you use the Search service (Mssearch.exe) to perform a search in SharePoint Server 2010. In this situation, the Search service (Mssearch.exe) stops responding.
To resolve this issue, apply the following update:
2553037 Description of the SharePoint Server 2010 hotfix package (Osrchwfe-x-none.msp): August 30, 2011
Microsoft has confirmed that this is a problem in the Microsoft products that are listed in the "Applies to" section.