I created this timelapse the same as all the others I've done but this message came up.

Normally with LRT3 you start the rendering from Lightroom, by using the LRTExporter plugin - this will create an intermediate JPG or TIF sequence und hand that over to LRT and the render dialog automatically pops up and renders the final video.

In your case you oviously manually selected "render" from the File menu in LRTimelapse, this is only meant to be done, if you already have an intermediate Sequence, that you want to render again - thus the render dialog only allow to select thos intermediate sequences, not "RAW"-sequences.

Just go the route vial the Lightroom Library Export and the LRTExporter plugin.

Actually it had to do with the way some photos in my sequence were named. One of my sequences got to 999 so it started over at 1 in a new folder on my camera so I renamed the last photos so they were at the beginning of the folder. LRtimelapse didn't like that for some reason.