I run OSX 10.10.5 on an early 2011 MacBook Pro, and just upgraded to Skim 1.4.35. The same problem appeared on the earlier version of Skim, however. "Skim Quit Unexpectedly: Click Reopen to open the application again. Click Report to see more detailed information and send a report to Apple" comes up every time I close a pdf that happens to have highlights in it. Pls see crash report attached.
I also just upgraded to 1.4.35, and am also having this issue. It didn't occur in the last version for me, though. I'm running OSX 10.10.5 on an early 2015 Macbook Pro.
This is a duplicate of bug # 1260