You must remove a certificate before removing its associated request.
To remove a certificate request:
Start Oracle Wallet Manager.
(UNIX) At the command line, enter the following command:
owm
(Windows) Select Start, Programs, Oracle-HOME_NAME, Integrated Management Tools, Wallet Manager
If the wallet is closed, then open it by selecting Open from the Wallet menu. When prompted, select the wallet directory location, and then enter your wallet password.
In the left panel subtree, select the certificate request that you want to remove.
From the Operations menu, select Remove Certificate Request.
In the Confirmation dialog box, click Yes.