Whilst you may be correct in some circumstances there are problems I have encountered. Please check out my latest conversation titled '200.2.5 Win OS upgrade'
I went from CCM 3.0(1) to 3.2(3) over 3 yrs and when I apply 2000.2.4 or 2000.2.5 then I encountered a problem viewing admin or user pages. Yet CCM was working without issues, just that I couldn't view ccmadmin/ccmuser.
I will be interested in what the IWAM and IUSR accounts you see on your Call Managers are...Mine are IWAM_Guest and IUSR_Guest and during the upgrade the accounts being used are changed to IWAM_Spirian and IUSR_Spirian. This means that when the IIS web pages are viewed, Call Manager has the incorrect account info and hence the message 'HTTP 500 Internal Server Error'
Are you getting this error “Installer User Interface Mode Not Supported. The installer cannot run in this UI mode. To specify the interface mode, use the -i command-line option, followed by the UI mode identifier. The value UI mode identifiers...
The below trick might come handy when you have to add a new node to a cluster but you don't have or is unsure of the security password for the publisher. This procedure has been around for ages.
1) Login into the CLI of the Publisher.