Based on the fact that its a DCOM error, I would assume that you may just need to "open up" your DCOM settings, at least for the service that is being accessed. I am assuming that the software you are using is all on one computer, otherwise you may have to do this on the computer with the 'server' application.

Start by going into your DCOM config (dcomcnfg.exe from the Run command). If this is in XP, then you'll have to drill down through Component Services...Computers...My Computer... then to DCOM Config. Expand DCOM Config and you should see a list of applications. Try to find the application in the list that would be doing the firmware update. Maybe it starts with Rockwell, or Allen-Bradley, or it might not actually have a name - it might just have {5A5AA0AA-1DEB-4683-96B0-B43301E83971} for a name, judging by your error.

When you find the application in the list, right-click and go to Properties. Here's where you can tweak the settings. I would try (on the General tab) changing the Authentication Level to None, and see if that helps. Also you can try (on the Security tab), selecting Customize for each permission type, then click Edit for each and add the user "Everyone", and give that user full permissions.

If that doesn't do it, I would call Rockwell support.