Checkbox Does not post

Hi Sir.
This plugin is great I will be very thankful to you if you solve this problem in plugin.
Contact form Code:
<p>Select Items [checkbox dress use_label_element "All" "Casual" "Social" "Summer" "Maxi"]</p>
Form to Post Code:
Dress Types: {$form_data->posted_data['dress']}
When I submit CF7 with above checkbox code and put above form to post code It does not post the checkbox items and instead post “Array”
Am I making some mistake?
I need these checkbox and I want to post at least 10 items at a time through these checkbox.