[TYPO3-mvc] error in TCA: (travel) Probably value mismatch with fieldtype.

[Domi]

Hello,

I try to set up an extbase extension for a travel agency.

I set up two relations, that I can edit the relations in Travel as well 
as in City:
1:n City - Travel
n:1 Travel - City

I need to set up city that multiple select is possible but I get 
following error:

102: These fields are not properly updated in database: (travel) 
Probably value mismatch with fieldtype.

This is my TCA where I try to get multiple selection work, but everytime 
I try to assign more than one travel to a city the error occurs.

$TCA['tx_dmftravelagent_domain_model_city']['columns']['travel'] = array(
     'exclude' => 0,
     'label' => 
'LLL:EXT:dmf_travelagent/Resources/Private/Language/locallang_db.xml:tx_dmftravelagent_domain_model_city.travel',
     'config' => array(
	'type' => 'select',
	'internal_type' => 'db',
	'allowed' => 'tx_dmftravelagent_domain_model_travel',
	'foreign_table' => 'tx_dmftravelagent_domain_model_travel',
	'size' => 15,
	'minitems' => 0,
	'multiple' => 1,
	'autoSizeMax' => 20,
	'maxitems' => 150,
	'wizards' => array(
		'_PADDING' => 1,
		'_VERTICAL' => 1,
		'edit' => array(
			'type' => 'popup',
			'title' => 'Edit',
			'script' => 'wizard_edit.php',
			'icon' => 'edit2.gif',
			'popup_onlyOpenIfSelected' => 1,
			'JSopenParams' => 'height=350,width=580,status=0,menubar=0,scrollbars=1',
			),
		'add' => array(
			'type' => 'script',
			'title' => 'Create new',
			'icon' => 'add.gif',
			'params' => array(
				'table'=> 'tx_dmftravelagent_domain_model_travel',
				'pid' => '###CURRENT_PID###',
				'setValue' => 'prepend',
				),
			'script' => 'wizard_add.php',
		),
	),
     ),
);

Does anybody can help me out?

THX
Dominic