You cannot remove a trusted certificate if it has been used to sign a user certificate still present in the wallet. To remove such trusted certificates, you must first remove the certificates it has signed. Also, you cannot verify a certificate after its trusted certificate has been removed from your wallet.
To remove a trusted certificate from a wallet:
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.
Select the trusted certificate listed in the Trusted Certificates tree.
From the Operations menu, select Remove Trusted Certificate.
A dialog box warns you that your user certificate will no longer be verifiable by its recipients if you remove the trusted certificate that was used to sign it.
Select Yes.
The selected trusted certificate is removed from the Trusted Certificates tree.