error in text determination procedure

hi gurus

i have defined text determination procedure from customer master to sales order and it works fine, when i am defining a text det procedure for delivery document i have referenced the text from sales order. i am able to define it but while assigning it to the Delivery doc type it says the text procedure is not defined. i can cleary see the text procedure ( It can be seen in F4 also) and i am sure all the settings are in place. Can anyone guess what could be the reason for this error?

Thanks in advance

Srini