I'm having some issues with my site, the front end all works fine, I cannot access anything on the administrative side (accessing the Dashboard)

I've got the server error using:

site.com/index.php/tools/required/themes/preview_internal?themeID=1&previewCID=1


Fatal error: Uncaught exception 'Exception' with message 'Access Denied' in /services3/webpages/t/a/taitcc.com/public/main/updates/concrete5.4.2/concrete/tools/themes/preview_internal.php:19 Stack trace: #0 /services3/webpages/t/a/taitcc.com/public/main/updates/concrete5.4.2/concrete/startup/tools.php(13): include() #1 /services3/webpages/t/a/taitcc.com/public/main/updates/concrete5.4.2/concrete/dispatcher.php(146): require('/services3/webp...') #2 /services3/webpages/t/a/taitcc.com/public/main/concrete/startup/updated_core_check.php(6): require('/services3/webp...') #3 /services3/webpages/t/a/taitcc.com/public/main/concrete/dispatcher.php(14): require('/services3/webp...') #4 /services3/webpages/t/a/taitcc.com/public/main/index.php(2): require('/services3/webp...') #5 {main} thrown in /services3/webpages/t/a/taitcc.com/public/main/updates/concrete5.4.2/concrete/tools/themes/preview_internal.php on line 19