It seems you created a file with a backslash in the name. That’s not an acceptable character for file names, and behavior surrounding such files may be inconsistent.
And it seems that while PHP lets you create such files without any problems, FTP (and the file manager) do not.
I think the best way to remove this file is through PHP. To do so, create a PHP file in the same folder as this file, say, deletefile.php
with the following contents:
<?php
if (unlink('utils\gallery.sqlite')) {
echo "File deleted!";
} else {
echo "Unable to delete file!";
}
Then, open access this file from your browser (like http://example.com/deletefile.php
).