Thread:Extension talk:CirrusSearch/Installationproblem again - look to error-file (win7 64bit)/reply (2)

That error looks like your PHP install does not include the curl PHP extension. The  function is provided by that extension. Your PHP is not finding that function in the global scope or in the local namespace of the Elastica\Transport\Http class and reporting the function as missing in the class namespace. See a tutorial like http://www.tonyspencer.com/2003/10/22/curl-with-php-and-apache-on-windows/ for help installing and configuring curl for PHP on Windows. You will know you have it installed when  includes.

The CirrusSearch extension requires curl support to communicate with the backend Elasticsearch server.