Even when Steam added support for multiple game 'libraries', there always seemed to be a few games that do not support being located anywhere but the default directory.
However, it is always possible to move the files yourself manually, and create a link back to them from their original location. This way, Steam thinks that it's still in the same location, and your SSD has less clutter on it.
Shut down Steam (make sure it isn't still in your notification tray)
Cut the game's install directory from
Paste the game directory where you want (e.g.
Open a Command Prompt Window and navigate to where the folder was, i.e.
Create a directory symbolic link with the same name as the original folder using the
mklink command. The format is like so:
mklink /D "<Folder Name>" "<Path To Moved Folder>"
mklink /D "Half Life 2 Episode One" "E:\Games\Half Life 2 Episode One"
If you now look at the
steamapps/common directory in Windows Explorer, you will see what looks like a shortcut icon. Double clicking it will take you to the folder located on the
Start Steam again and you will be able to play the game normally, as far as it is concerned the game hasn't moved.