Hi Michael, Paul,
The most probable cause, of the issue that you are experiencing, is the fact that the databases are not read. Steel Connections installs some databases in "c:\ProgramData\Autodesk\Revit Steel Connections 2018\en-US".
There are 2 scenarios in which this can happen:
1. You installed a Preview Release version of Revit 2018, uninstalled it and then installed the official Revit 2018 version. In this case the .ldf keys that are used to open the databases are from the Preview Release and Revit 2018 official can't use them to open the databases. To fix this case you will need to open "c:\ProgramData\Autodesk\Revit Steel Connections 2018\en-US" folder and delete all the .ldf keys. Once you open a Connection Dialog or the Connection Settings dialog, new ldf keys will be generated automatically.
2. You don't have SQLLocalDB installed. Please install ENU\x64\SqlLocalDB.msi from the following location
https://www.microsoft.com/en-us/download/details.aspx?id=46697
If you have Office x64 then you can proceed to install the downloaded SQLLocalDB x64.
If you have Office x86 then SQLLocalDB x64 must be installed in silent mode, from command prompt.
Try to fix the issue with these steps, if you hit any problems don't hesitate to post again, and I will help you.
Regards,
Mihai Sandu
Sr. QA Analyst