2 plugins enabled
Nextgen conflicts with plugins that use session_start - it will generate an error such as:
Warning: session_start() [function.session-start]: Cannot send session cache limiter - headers already sent (output started at .../wp-includes/functions.php:2944) in .../wp-content/plugins/si-contact-form/si-contact-form.php on line 2157
In this case the other plugin is Fast Secure Contact Form. If I disable Nextgen the error goes away.
I suspect there is a stray blank space somewhere outside the PHP tags. This was not a problem with the previous version of Nextgen that I used (which might be 1.9.6 but I'm not sure).