Credit note button disabled

Hii all,

Here is an issue. 

After doing an invoice in Purchase order, the credit note button is becoming disabled. It is remaining enabled till the received status.

As per the concept i got, i guess the credit note button should remain enabled even after Invoice. I am using AX 2012.

Please help in resolving this issue. And correct me if i have went wrong anywhere. Thanks in advance.

Thanks and regards,

Parashar Banerjee.