although we don't have 2012R2 running wit FMS10, You might have problems installing/configuring an older FMS version. Current browsers might not work (admin console can't be initalized). Due to java, administrating the server from a (current OS) client might be a problem as well.
We've been running into issues with 2008 and FMS11 as well... There will be little support -if any- with this configuration. We got OSX 10.11 sites running FMS10 - the server is running, but no way to get access to the admin console...
not that I love to say it - but I strongly recomend to upgrade to a current version of FMS (and clients..). We got 2 FMS working under 2008R2 and current browsers/java - but they are making troubles after a couple of days (no more backups, although the server itselfs is running fine)
Markus, thanks for your thoughts on this. I am prepping my client to consider the upgrade right now. It is just to much of a headache. On my end the server runs great when it is manual started, and back ups work. But, for some reason. The server just closes, loses contact and cannot restart after the files are saved to disk. I have to manual start the server. I have tried a script to start server, but fails as well. It thinks the server is running, when in actually it is not.
I really appreciate your thoughts, big help.