Hi @ruenel,
Well, I removed the previous code, i.e.;
add_filter( ‘upload_mimes’, ‘cs_fix_upload_mimes’, 999999 );
function cs_fix_upload_mimes ( $mimes ) {
$mime_types = array(
'woff2' => 'application/octet-stream',
'woff' => 'application/font-woff',
'ttf' => 'application/x-font-ttf'
);
if ( apply_filters('cs_font_manager_add_legacy_mime_types', false) ) {
$mime_types['svg'] = 'image/svg+xml';
$mime_types['eot'] = 'application/vnd.ms-fontobject';
}
return apply_filters( 'cs_font_manager_mime_types', $mime_types );
}
And replaced it with your new code, i.e.;
add_filter( ‘upload_mimes’, ‘cs_fix_upload_mimes’, 999999 );
function cs_fix_upload_mimes ( $mimes ) {
$mime_types['woff2'] = 'application/octet-stream';
$mime_types['woff'] = 'application/font-woff';
$mime_types['ttf'] = 'application/x-font-ttf';
if ( apply_filters('cs_font_manager_add_legacy_mime_types', false) ) {
$mime_types['svg'] = 'image/svg+xml';
$mime_types['eot'] = 'application/vnd.ms-fontobject';
}
return apply_filters( 'cs_font_manager_mime_types', $mime_types );
}
And it still gave the security permissions error when I tried to upload a jpg, see image below;
I’m really struggling to understand what is causing the problem now 
Thank you for your continued assistance resolving this.
Paul.