Ran, please download and reinstall the latest launcher. If the update fails, press OK to try again and the second time it won't timeout.
jayman1000, your crash is different. The update is downloaded and run, then crashes. I am uploading 1.8.39 right now which may fix this. For now you can put the text "1.8.35" into your version.txt file here:
Windows: <user home folder>\Spine\version.txt
Mac: <user home folder>/Library/Application Support/Spine/version.txt
Linux: <user home folder>/.spine/version.txt
Please create the file if it doesn't exist. This will cause Spine to use 1.8.35 and not the latest. You will need to delete the version.txt or click Spine, Settings and change "Update" to "Latest".
1.8.39 is now up, but there is still a problem. At least I can see it, so I can work on fixing it. I've reverted Essential on Windows to 1.8.35, everyone else is on 1.8.39 until this is fixed. Sorry!