First of all make sure that Render[IN] 3 is recording logs.

From the Extension menu navigate to Render[IN] 3 then make sure that Logs are checked in in the palette.

If any error occurs Render[IN] 3 will record some data into a text document.

To force the new data to be written, you have to re-launch SketchUP first before collecting the document.

After relaunching SketchUP, activate the Render[IN] 3 preview for a while then you can close it.

You can now locate the fresh logfile.

On PC:

C:\Users\Your User Name\Renderin3.log


Macintosh HD/Users/Your User Name/Renderin3.log