Everything looks correct to me. I'll try it myself a little later today and let you know how I make out.

Ok, many thanks!

Seems the updateCMSFields() gets called when going to admin/assets/ and since it's trying to add a new textfield to a Root.Main tabset and it doesn't exist it breaks. Try this

public function updateCMSFields(FieldList $fields) {
        if($fields->hasTabSet('Root.Main')){
            $fields->addFieldToTab('Root.Main', new TextField('Description'));
        }
}

HI IOTI, now it works like a charm. Something i will use over and over.

Combined witht the function that alows me to select an image folder for a typical page, it generates a list of images from a folder that i can easily place into a Jquery image gallery and have to variables to use: $Description and $Client.

Its like an image gallery module for SS3 without being one!

<% control ImagesIDE %> <!-- generates images from selected folder into the page's CMS panel -->
       <!-- look for $Description and $Client as inserted into the FIles image panel -->
	<img src="$URL" alt="{$Description}<br /><strong>{$Client}</strong>" title="" /> 
<% end_control %>

As seen here (view of the Image File panel)

Many thanks!