I just updated from Atahualpa 3.4.9 to 3.6.4 through the WP Control Panel and started getting the following message in my browser:

FastCGI Error
The FastCGI Handler was unable to process the request.

Error Details:

* The FastCGI process exited unexpectedly
* Error Number: -1073741819 (0xc0000005).
* Error Description: Unknown Error

HTTP Error 500 - Server Error.
Internet Information Services (IIS)

My troubleshooting so far:

• Manually uploaded 3.4.6 and 3.6.4 into separate folders: 3.4.6 is fine, 3.6.4 is not
• The problem continues even with all plugins disabled, so unlikely to be a conflict with plugin stylesheets
• I have not manually edited any of the files: changes only done through the Atahualpa settings
• Tech at my hosting company got snarky when I asked about server side FastCGI issues: after all, if one site works and one doesn't (albeit with different WP and Atahualpa versions) it is unlikely to be server side.
• The tech linked me to a Microsoft Knowledge Base article that suggested it could be an issue with incomplete <SPAN> tags - unfortunately I have mislaid the link
• "Delete the option 'bfa_ata4" and "Reset all theme options" have no effect either

Do you have any idea what might have changed between 3.4.6 and 3.6.4 to cause this problem?
Thanks in advance.

For what it's worth the site (on 3.4.6) is at http://www.knottinbotswana.com

a major change in 3.6 is the elimination of the php eval() functin and it's replacement with stream wrappers. Some hosts have 'Suhosin' added to their PHP which can cause some conflicts. You can check out the thread Try this if you are getting blank page with Atahualpa 3.6.x and ask your support about suhosin to see if this is the cause