by Hartmut Scherer.
Hi Syed,
If you want to use your customized theme in Moodle 2.7, you need to add a version.php page (use the version.php of the base theme as an example). You also need to change the config.php in your custom theme (delete all references to standard or other themes that are no longer in Moodle 2.7). Then, you should be able to use your customized theme again.
With kind regards,
Hartmut