Laura,

We have recently changed the Plan Graphics dialog to being HTML, which requires multiple files to download.
Located in your Landfx/data folder, there should be an html sub-folder, and within there is a content_generic folder. A missing file error means that one or more of these folders was unable to be created, or the files were unable to download.
You can make sure the folders are there, or can be created, and you have permissions to save files there.

--J