Problem related to Customised IDOC

Hi,

I am facing one problem related to customised IDOC.

Currently we are Upgrading SAP from 4.6 C to ECC 6.0. The development ECC6.0 system has been copied from SAP 4.6C development system. When I try to modify the customized IDOC segment fields in ECC 6.0 development system , it is not allowing me to modify it. I tried to cancel the release of basic IDOC type & segment type but It gives me the message that IDOC has already been release in SAP4.6C system.

I have tried everthing to modify the customized IDOC such as Cancel release & Set Release but unable to change it.

Can any body suggest how to modify the customized IDOC segment as I am not

Thanks & Regards

Prabhat Ranjan