macOS Mojave (10.14.6), first time running Squeak file. Steps to reproduce:
1. Download Squeak dmg file to Downloads folder.
2. Double-click on downloaded dmg file.
<img src="http://forum.world.st/file/t370088/Screen_Shot_2019-09-20_at_09.png" border="0" alt="Screen Shot of error message"/>
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