On analyzing SharePoint search crawl logs, found many instances of the error: “The filtering process could not be initialized. Verify that the file extension is a known type and is correct”
This is because, SharePoint server 2007 search crawler doesn’t recognize Office 2010 file types (such as .docx, .pptx, .xlsx,etc).
Solution: Download and Install Office 2010 Filter pack from http://www.microsoft.com/en-us/download/details.aspx?id=17062 to the Index server.
This filter pack installs a few dlls and fixes the above issue. If you happen to see this error on PDF documents, make sure you have PDF IFilters installed and configured.