This is not a folder: /var/www/clients/client6/web41/web/fw2/sites/default/files/photoalbum//Gitar_Bassgitar/. Set the right folder in settings of Smplphotoalbum
There is no cache folder or not writable: /var/www/clients/client6/web41/web/fw2/sites/default/files/photoalbum//Gitar_Bassgitar/_tn_
Error message
Warning: mkdir(): No such file or directory in Drupal\smplphotoalbum\ImageList->__construct() (line 132 of modules/smplphotoalbum/src/ImageList.php).
Warning: scandir(/var/www/clients/client6/web41/web/fw2/sites/default/files/photoalbum//Gitar_Bassgitar/): Failed to open directory: No such file or directory in Drupal\smplphotoalbum\ImageList->__construct() (line 180 of modules/smplphotoalbum/src/ImageList.php).
Warning: scandir(): (errno 2): No such file or directory in Drupal\smplphotoalbum\ImageList->__construct() (line 180 of modules/smplphotoalbum/src/ImageList.php).
Warning: foreach() argument must be of type array|object, bool given in Drupal\smplphotoalbum\ImageList->__construct() (line 190 of modules/smplphotoalbum/src/ImageList.php).
