Ran into the same problem. A solution is here http://www.tpateman.co.uk/reboot/error-activating-jetpack-plugin/ but I would hope the plugin author would build in a workaround. Seems like a PHP 5.4 cert validation function believes the SSL from wordpress.com isn’t valid.
When running WordPress on IIS 7 you also have to change the max request size in web.config like so:
<?xml version="1.0" encoding="UTF-8"?>
<configuration>
<system.webServer>
<security>
<requestFiltering>
<requestLimits maxAllowedContentLength="10000000" />
</requestFiltering>
</security>
</system.webServer>
</configuration>
The value is in bytes.
I ran into this same issue and I was able to solve it by changing the limits in php.ini and web.config. The change in max size was reflected in the WordPress upload page. If the value in the upload page doesn’t change you might be editing the wrong php.ini (I had two instances of the file in two distinct PHP install directories).
