I came across an interesting error in my labs today, I already had a 2012 domain with 2 DCs that has been working happily but decided to add a 2012 R2 DC to the mix.
However, when I tried to do so I was presented with the following error during the prerequisite stage: Unable to perform Exchange schema conflict check for domain. Exception: A security package specific error occurred. Adprep could not retrieve data from the server through WMI.
After a bit of research I kept coming across the same issue but when adding a 2012 DC to a 2003 forest. I tried all the suggestions on that to be on the safe side but nothing seemed to be working for me. In particular I pondered on one of the solutions to the 2003 issue which was to add a 2008R2 server to the domain to upgrade the schema. After thinking about things I wondered if the issue was indeed the schema version. Whilst it should support at least one version back I thought I would check it out. I ran the following command to get my current schema version:
I figured why not and ran adprep on my schema master from the 2012 R2 media. (<mediadrive>:supportadprepadprep /forestprep, followed by <mediadrive>:supportadprepadprep /domainprep – gpprep isn’t needed as no gpos are updated).
After that it successfully passed the prerequisites.