multisite->singlesite error

Hi,

I migrated my website from WP multisite to singlesite. Now, when activating WooCommerce I gen an error:

Warning: array_key_exists() expects parameter 2 to be array, bool given in /var/www/clients/client1/web43/web/wp-content/plugins/woocommerce/includes/admin/helper/class-wc-helper-options.php on line 54
Call Stack
#	Time	Memory	Function	Location
1	0.0033	394216	{main}( )	.../tools.php:0
2	0.0033	394952	require_once( '/var/www/clients/client1/web43/web/wp-admin/admin.php )	.../tools.php:40
3	2.3902	41131888	do_action( $tag = 'admin_init' )	.../admin.php:175
4	2.3902	41132264	WP_Hook->do_action( $args = [0 => ''] )	.../plugin.php:484
5	2.3902	41132264	WP_Hook->apply_filters( $value = '', $args = [0 => ''] )	.../class-wp-hook.php:311
6	2.4183	41430296	Automattic\WooCommerce\Admin\Notes\WooSubscriptionsNotes->admin_init( '' )	.../class-wp-hook.php:287
7	2.4183	41430296	Automattic\WooCommerce\Admin\Notes\WooSubscriptionsNotes->check_connection( )	.../WooSubscriptionsNotes.php:77
8	2.4183	41430296	Automattic\WooCommerce\Admin\Notes\WooSubscriptionsNotes->is_connected( )	.../WooSubscriptionsNotes.php:106
9	2.4183	41430296	WC_Helper_Options::get( $key = 'auth', $default = ??? )	.../WooSubscriptionsNotes.php:125

( ! ) Warning: array_key_exists() expects parameter 2 to be array, bool given in /var/www/clients/client1/web43/web/wp-content/plugins/woocommerce/includes/admin/helper/class-wc-helper-options.php on line 54
Call Stack
#	Time	Memory	Function	Location
1	0.0033	394216	{main}( )	.../tools.php:0
2	0.0033	394952	require_once( '/var/www/clients/client1/web43/web/wp-admin/admin.php )	.../tools.php:40
3	2.3902	41131888	do_action( $tag = 'admin_init' )	.../admin.php:175
4	2.3902	41132264	WP_Hook->do_action( $args = [0 => ''] )	.../plugin.php:484
5	2.3902	41132264	WP_Hook->apply_filters( $value = '', $args = [0 => ''] )	.../class-wp-hook.php:311
6	2.4183	41430296	Automattic\WooCommerce\Admin\Notes\WooSubscriptionsNotes->admin_init( '' )	.../class-wp-hook.php:287
7	2.4190	41430832	Automattic\WooCommerce\Admin\Notes\WooSubscriptionsNotes->is_connected( )	.../WooSubscriptionsNotes.php:79
8	2.4190	41430832	WC_Helper_Options::get( $key = 'auth', $default = ??? )	.../WooSubscriptionsNotes.php:125

Removing and re-installing WooCommerce Plugin does not help. Any ideas, what went wrong here?

Thx, Stefan

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