Did you do an uninstall of FMS 11 before the installation of 12?
It is common for there to be conflicting pieces of stuff in the system when upgrading FM Servers if you do not perform a full uninstall before the new installation.
If that was the case, try doing an uninstall of BOTH, then do the new installation of 12.
Another thought: Be sure to do a full install of 12 or you may be missing some of the Web Publishing pieces. Full installs were required for WP in 11, and probably still are in 12.
Yes, I uninstalled 11 before installing 12. However, as you suggested, ran an uninstall on both versions then a reinstall of 12.
No luck. Same error message in console.
Also, because the FMS installer altered the apache httpd.conf file, I can no longer turn on Web sharing in the Sharing preferences pane.
Shot in the Dark:
In older versions of FM Server that config file error was associated with Apache failing to start.
I am unable to find a reference to this for Server 12 yet. FMI generally tries to cover this type of stuff in KnowledgeBase, so it may be worth contacting them for installation support.
OK, I've found the solution…
Even after running uninstalls for both FMS 11 and 12, there was still a folder called Filemaker Server with stuff in it in the system Library. I trashed it. Then I went to private/etc/apache2, deleted the httpd.conf, which the FMS installer had altered, duplicated the file httpd.conf.default and renamed it httpd.conf. This restored the Lion Web sharing.
Then a fresh install of FMS 12 and I'm up and running.
Hope this is helpful to anyone who runs into a similar situation.