OK - I have a fresh 3.0.1 install and with UndefinedOffset version

it shows the widgets on the left (under Available widgets)
but when I click on them they are not transfered to the right (Widgets currently used) instead I see the following...

First question, have you done a dev/build?flush=all

Second, could you copy/paste the entire content of that notice? It now only shows the first part of the string.

First question, have you done a dev/build?flush=all

yep

Second, could you copy/paste the entire content of that notice? It now only shows the first part of the string.

ok, so how lazy was I? Also how much of a pain is moving to SS3 going to be *sigh*

so my problem was...

		return new FieldSet(
			new TextField('Text', _t('IEDectiontionWidget.TEXT', 'Text to show in the widget and alert'))
		);

needed to be...

		return FieldList::create(
			TextField::create('Text', _t('IEDectiontionWidget.TEXT', 'Text to show in the widget and alert'))
		);