problem with multiColumnWizard & checkboxWizard

Hello everyone,
I m new with contao that I just discovered thanks to the work placement I m currently doing and I have a lot of troubles trying to do the following thing :

I m developping a module to generate proposals and those proposals are composed by services which may or may not contain subservices, see :

http://imageshack.us/photo/my-images/21 ... epage.png/

So this is my services page where the user can edit a services and its subservices, as you can see I m using multiColumnWizard for the subservices as I want to change their order easily so in my databse the subservice field and my services table looks like this :

http://imageshack.us/photo/my-images/52 ... bserv.png/

Now my problem is I can't retrieve my subservices on my proposal page, where I d like to use a checkboxWizard to make the selection easy for the user, like on this homemade picture :

http://imageshack.us/photo/my-images/86 ... lpage.png/

I think the problem is that the ' foreign key ' attribute is waiting for sql but as the information I want is on a text field with the multiColumnWizard syntax and I don t know how to do it another way.

Thanks for your help, sorry for my poor english and don t hesitate to ask me more details if something isn t clear.