Im using a Mac with Mavericks
On going to export from LR5 I get the following message at the bottom of the export window beside the Plug In Manager button:
Unable to export The "nil" plug-in is not installed or not functioning properly.

I have no clue how to fix this.

Issue has now been resolved. I had LR5 open in error while installing LRT 3

Glad you sorted it out.