Description:
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The environment is PHP official-compiled VC9 5.4.9 NTS running on IIS 7.5 using 
FastCGI, and Wincache 1.3.4.1 is selected to be the session handler.
When access PHPMyAdmin with IIS basic authentication enabled, wincache will 
sometimes fail to initialize the session after logged in PMA.

Test script:
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phpMyAdmin\libraries\session.inc.php 

Expected result:
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HTTP 200 OK

Actual result:
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HTTP 500 with the following logged error message.
session_start(): Failed to initialize storage module: wincache