You have to use the FORCE option to remove a GENREQed certificate.
TSS REM(Myacid) DIGICERT(Mydcert) FORCE
Be careful before removing with FORCE a certificate.
If the certificate has not been added back once it has been signed by a CA, the private key will be lost.
If the signed certificate has been added back to its original acid then private key has been reconnected, then FORCE can be used to remove the GENREQed certificate.
If the certifcate is not signed and is not use, then FORCE can be used.