[TYPO3-mvc] Fluid form don't work with objectStorage

[Pascal Geldmacher]

Hey,

I've a Model Post that has some attributes like title(String), 
description(String), tags(Storage), categories(Storage) etc.

if i only want save title and description in my database it works fine 
without problems. So but if i use checkboxs to select many tags or 
categories to save that with the title and the description in the 
database i've got the error that my createAction method needs a Post 
object and i gave him an array. That make no sense ? Or what must i do 
that it will running.

Thats my fluid form. It's a part from the whole form. It has some 
special attributes cause thats an extJS form.

<blog:form action="create" controller="Post" div="tx_mfblog" 
formTitle="create a new Post" targetController="Post" 
targetAction="index" name="post" arguments="{blog: blog}">
		<blog:textbox property="title" label="Post title" allowBlank="FALSE" 
textFieldSize="250" labelSize="80" />
		<blog:textarea property="description" label="Description" 
allowBlank="FALSE" rows="250" cols="80" labelSize="80" />
		<blog:textbox property="author" label="Author" allowBlank="FALSE" 
textFieldSize="100" labelSize="80" />
		<blog:label text="Select Categories" width="250" />
		<f:for each="{blog.categories}" as="category">
		<blog:checkbox property="categories" value="{category.uid}" 
label="{category.name}" labelSize="80" />
		</f:for>
</blog:form>

I hope you can help me.

Thanks a lot
Pascal