SSL certificate is reported as invalid by iDRAC7

I'm trying to install a wildcard certificate (*.my.example.com) to an iDRAC6 - this cerificate was provided by RapidSSL (a subsidiary of GeoTrust) and is used across our ubuntu/apache webservers and other things, but I'm having trouble deploying it to an iDRAC which needs it.

So far, I've uploaded the key and certificate using Dell's idracadm software on Ubuntu:

> sudo /opt/dell/srvadmin/bin/idracadm -r idrac.my.example.com -i sslkeyupload -t 1 -f wildcard.my.example.com.key

< SSL key successfully uploaded to the RAC.

> sudo /opt/dell/srvadmin/bin/idracadm -r idrac.my.example.com -i sslcertupload -t 1 -f wildcard.my.example.com.crt

< Certificate successfully uploaded to the RAC. The RAC will now reset         
< to enable the new certificate and may be offline temporarily.

I wait a short time, then try to use sslcertview to confirm the certificate, but I get:

< Security Alert: Certificate is invalid - unable to get local issuer certificate

I also get security warnings in Firefox - saying the issuer is unknown (but the rest of the details seem correct). So, I'm trying to get the CA certificates for RapidSSL and GeoTrust using:

> sudo /opt/dell/srvadmin/bin/idracadm -r idrac.my.example.com -i sslcertupload -t 2 -f intermediate.crt

But I get told the upload was unsuccessful as this certificate is invalid.

I've also created a PKCS#12 file with the key, certificate, and intermediates to upload, but this is not being upload either.

I'm using iDRAC7 with firmware 1.57.57

How do I resolve this?