Thanks till for finding this:
If I comment out the following lines in the english
language file /home/admispconfig/ispconfig/lib/lang/en.lng:
$wb["txt_object_currently_updated"] = "Your changes cannot be saved because this item is currently being updated. Please try again later.<br><br> <a href='../frame_start.php?s=$s'>Next >></a>";
$wb["txt_system_currently_updated_no_recycle_bin"] = "The recycle bin cannot be accessed because the system is currently being updated. Please try again in a few minutes.<br><br> <a href='../frame_start.php?s=$s'>Next >></a>";
$wb['no_permission_to_change_data'] = "<b>Error: You don't have the necessary permissions to change these data.</b><p>
This is because of one of the following reasons:<br>
1. You are using the system in test mode.<br>
- Log in with your username and password.<br> <br>
2. You are trying to change an element which is allocated to another group.<br>
In this group you don't have permission to write / edit data.<br>
- Please ask the owner of the group to grant write access to this resource to you.<br> <br>
<center><a href=\"" . $go_info["server"]["server_url"] . "/index.php?s=$s\">Next >></a></center>";
everything is working fine. But the lines do not contain a syntax error, so I guess it must be a bug in the PHP interpreter itself, as it fails when it shall replace the $s variables.
It does not affect your sytstem when these lines are commented out in en.lng, as your system is set to french locale and the en.lng file is only loaded for the remoting part and the remoting part does not need these 3 lines.