SharePoint Search Error : "The protocol handler cannot be found. Check that the handler has been installed."

This issue occurs when the "mssph.dll" (Search Protocol Handlers) is not registered for searching the content sources.

Try :

Start-->Run

regsvr32 "C:\Program Files\Common Files\Microsoft Shared\web server extensions\12\BIN\mssph.dll"

Try Full crawl and it should work.