Looks like it is a style from your old UBB version.
Somehow it is hosed.
Might be due to ubb 7.6 is not compatible with php 7.x
If it were me I would downgrade php back to 5.4
Reload a backup of your files and database.
Ensure all file and folder permissions are correct according the document for install.
Make sure it is working correctly
While you are at this point you may want to check for that file but it would normally be like ubbthreads_1617365481.css without the php
Then upload your ubb7.7.5 files per the upgrade document
run install/upgrade.php
Then switch php to 7.x
Last edited by Ruben; 04/02/2021 1:25 PM. Reason: corrected typo
