In one environment, I had to test the possibility of an eRoom upgrade not succeeding. As part of the test, I backed up the three SQL databases, and performed the upgrade successfully. However, as a back out plan, I uninstalled the upgrade and removed the IIS folder and Program Files folder that were called eRoom. This means that the entire application is now uninstalled. Then I restored the databases. After rebooting the server and started to install the Index Server, the following error appeared:
The Indexing Server shares registry entries and files with the eRoom Server. You may not install an Indexing Server on an eRoom Server that is newer.
To resolve this error, I removed the registry entries that are associated with the installation.
After removing the registry entries, the installation proceeded as normal.
On a side note, instead of creating a new eRoom, I elected to join an eRoom and selected the SQL server containing the restored databases. A message appeared indicating that a server of the same name existed, do you wish to continue. The response wass yes. eRoom installed successfully for this downgrade, backout plan.