If you are encountering errors when attempting to use the Place command, or seeing a blank swatches panel, most likely you are using font manager FontExplorer X and updated the plug-ins to the recent updated versions.
Seems there’s a bug, discovered on the Adobe Forums thread where I learned about the cause of the issue. A Twitter user posted the above screenshot from the built-in updater in Font Explorer X 3, although the plugins can’t actually be downloaded it seems.
I am running version 2 of FEX still, and never even saw the plugin updates in the manager, I had to download directly from the Font Explorer X website.
Hopefully Linotype will fix this soon. In the meantime, delete or disable the plugin until the fix is released to get your Place command and Swatch panel back to normal.