Hi Karl,
Looks like one of your files on the destination side couldn't be written onto. This might happen if the file on the right is locked. But even so, SyncToy should not crash in most cases.
Would be helpful if you can provide some more info:
- what's the sync partnership (sync/echo)
- are you able to determing which file or folder is causing the issue. One way would be to run Preview and watch out for errors. If on multiple Previews, same file/folder error, that could narrow down. If you find some such file, can you share if there's something special about the file - it's attributes, does it's name match with the name of some file or folder on the destination.
Thanks,
Sameer