If you are using NextGen Gallery for a longer time and you recently updated your blog or moved it from one hosting company to another, you may notice that instead of your images you can see [No template found] or [Not a valid template] message.
This issue is related to the template settings of your NextGen gallery plugin. The older versions of the plugin used to save the full path to the template file as they were located on the servers drive. One one of the pages I recently fixed, in the settings I found reference to the following template: /var/www/websiteName/very-long-path/singlepic.php. After the hosting company change, this path was not proper anymore.
If you are experiencing such an issue, the solution is simple. Log in to the WordPress admin console and switch to the Gallery -> Gallery Settings page. In various sections of the setting you will find the Template setting. I found it in Basic Thumbnails, Basic Imagebrowser, Basic Singlepic, Basic Compact Album and Basic Extended Album sections. I recommend to change this setting to the value of “Default”. There is also legacy version available in most cases, but this is not recommended. Please note that you have to save your changes. The Save button is located down at the end of the page, after a long break (significant amount of white space) and can be easily unnoticed. Once you will adjust your templates, your images should display properly.