Initial situation:

Some uninstalled smilies are in the "Smilies" folder on the FTP. One of them contains an umlaut "ü" in the file name (fahne_türkei.gif). This file has been there since 2016, and smilies have been added many times during this time. This file is currently NOT in use, not installed - it´s just there.

The server was recently switched to PHP 8.1

When creating new smilies in the ACP, I encountered the following error:

Whoops, looks like something went wrong.

(1/1) ContentErrorException

Warning: Undefined array key "flags/fahne_t??rkei.gif" in acp_icons.php line 414

at acp_icons->main('icons', 'smilies') in functions_module.php line 676

at p_master->load_active() in index.php line 81

This error occurred when sending the selected (other) new smilies.

When querying the files in the directory, the smilie engine under PHP 8.1 now seems to have a problem if special characters appear in the file names.

The problem was solved for me by renaming the problematic file.