Sidebar Content Box not editable - html

Question

I have built a custom theme for a client some 12 months ago and all was working fine until recently. My client is unable to edit the content in the widgets on his sidebar.
I have tried to add other text widgets to the sidebar and even those are uneditable.
I disabled all the plugins to see if any of those are the culprit and as such made zero difference. Incidentally all of the text widgets are displaying perfectly on the public side of the website but my client is unable to add or edit and text widget in the sidebar.
Here is a screeny showing whats going on...
Many thanks for any advice you can give in this.
Phillip Dews
EDIT
For those that require it. Here is the code from my custom theme....
functions.php
function paradisereloaded_widgets_init() {
register_sidebar( array(
'name' => __( 'Sidebar', 'paradisereloaded' ),
'id' => 'sidebar-1',
'description' => __( 'Add widgets here to appear in your sidebar.', 'paradisereloaded' ),
'before_widget' => '<section id="%1$s" class="widget %2$s">',
'after_widget' => '</section>',
'before_title' => '<h2 class="widget-title">',
'after_title' => '</h2>',
));
}
add_action( 'widgets_init', 'paradisereloaded_widgets_init' );
And now the
sidebar.php
<?php
/**
* The template for the sidebar containing the main widget area
*
* #package WordPress
* #subpackage paradisereloaded
* #since Paradise Reloaded 1.0.0
*/
?>
<?php if ( is_active_sidebar( 'sidebar-1' ) ) : ?>
<aside id="secondary" class="sidebar widget-area" role="complementary">
<?php dynamic_sidebar( 'sidebar-1' ); ?>
</aside><!-- .sidebar .widget-area -->
<?php endif; ?>