Unknown: Couldn't find relative frame: $parentDetails
 

Since 8.2 I'm getting this annoying, very unspecific error:
Line 578 in Buggrabber deals with embedded loading when Swatter or Stubby are present. But whether I enable or disable Swatter or Stubby doesn't make any difference.
Since enabling Stubby I'm getting this:
This might not even be related to Buggrabber, Swatter or Stubby but I have no idea what kind of parent frame to search for.

Line 578 is inside the ADDON_LOADED event for BugGrabber. The surrounding code deals with Swatter and Stubby, but it also triggers for every addon loaded before the code deals with Swatter or Stubby. Some other addon is creating that error and it looks like one of those frustratingly useless XML errors that 8.0 now pushes to the UI instead of quietly writing them to a file like before.

There was some frame changes in 8.2 and it looks like an addon isn't gracefully dealing with them. WoW\_retail_\Logs\FrameXML.log might have more info, but my suggestion would be to disable, reload, reenable each addon you have until the error goes away. My supplemental suggestion would be to try disabling the addon "Details!" if you have it installed first. The frame name could be a coincidence, but it's worth a shot to start there.