Can't add label to any field

When i try to add a field to a content type and want to edit the label, it will wont show the name given by me in the overview or when trying to create the content. For example when editing field_bandname and changing the Label to Bandname it still shows field_bandname in the content creation dialog. I also get the following message, which i dont really understand as iam not into php:

Der Standardwert den PHP Code bei ungültigen Werten zurückliefert
Erwartetes Format :

array(
  0 => array('value' => value for value),
  // You'll usually want to stop here. Provide more values
  // if you want your 'default value' to be multi-valued :
  1 => array('value' => value for value),
  2 => ...
);

How do i make the label thing work?