Management/KeyCertificate::get_certificate_list_v2() not working

Hi,

We are using iControl API for one of our very critical solutions. We are facing some issues while calling get_certificate_list_v2 method for one of our BIG-IP device, others are working fine.

BIG-IP Version : 11.5.4

SOAP-ENV:Server Exception caught in Management::urn:iControl:Management/KeyCertificate::get_certificate_list_v2() 
Exception: Common::OperationFailed 
   primary_error_code : -7 (0xFFFFFFF9) 
   secondary_error_code : 0
   error_string         :  

I have no clue about the issue. Your help on this would be highly appreciated.

Please find the snippet below:

sub SOAP::Transport::HTTP::Client::get_basic_credentials
{
    return "$sUID" => "$sPWD";
}

$KeyCertificate = SOAP::Lite
    -> uri('urn:iControl:Management/KeyCertificate')
    -> proxy("https://$sHost:$sPort/iControl/iControlPortal.cgi");
eval { 
    $KeyCertificate->transport->http_request->header(
    'Authorization' =>
    'Basic ' . MIME::Base64::encode("$sUID:$sPWD", '')
    ); 
    };

if ( $sMode eq "" )
{
    $sMode = "MANAGEMENT_MODE_DEFAULT";
}
$soapResponse = $KeyCertificate->get_certificate_list_v2(
SOAP::Data->name(mode => $sMode),
);
print Dumper $soapResponse->result;

Regards,

Prabir