<b>Now, THIS is really weird!</b>
If I use Your account and English as default language, it works!!!
If I use MY account and French language it does not!
Would you be able to find out if I change your default language to French?
This means that the regex used only works for EN language, right?
If it can help, Template edit in local language backend was possible with YT plugin BEFORE 2.1.9...Maybe it would be worth looking at older versions you had around those famous 2 preg_replace lines...
Here's what I found using the existing 2.1.6 plugin from the download area
2.1.6 $body1 = preg_replace('@<form\s[^>]*name="adminForm"[^>]*>?.*?</form>@siu', $buffer, $body);
2.2.0 $body1 = preg_replace('@<form\s[^>]*name="adminForm"[^>]*>([\w|\W]*)</form>@msu', $buffer, $body);
Definitely a difference, but I don't know enough about regexp...
UNLESS what is required is a LOCAL French version of the plugin language files...Can try to do this...
Philippe