It happens for all categories even for the OOB categories. when i try to move a phase from the initial phase to the next phase, this error occurs. Anyways i am on filling any fields except the one that is automatically filled up while you open the change..
Ok, see, that's not any more information. Unless you give me some specifics, I can't try to duplicate what you're asking about. If I can't duplicate it, I can't see what the system is doing when it kicks out that error.
So, walk me through your process... You open a new change. You fill in _what_ fields, with _what_ information? Then, what do you do to generate the error? Save? Options->Next Phase? Cancel/ok?
Once you've given me the steps of what you're doing, I can try to be of more help.