When using MBSA in an offline mode, it is sometimes required to download the catalogue file manually (due to firewall restricitions on some PCs etc) The below link will enable you to download it. I hope you will find this useful as I can never remember where this bad boy is :)
Thanks for this! Wsusoffline is currently having issues with downloading it.
"Thanks for this! Wsusoffline is currently having issues with downloading it."
This is case for several months now and not just currently.