You're probably experiencing this issue: https://github.com/OpenSmalltalk/opensmalltalk-vm/issues/260
Please confirm if that's the case. In general, it helps if you give a bit more information about the crash (VM, image, etc).
Also I suggest you use Installer ensureRecentMetacello to load Metacello 
instead of that snippet, because that snippet breaks WebClient and 
SqueakSSL by loading an older, incompatible version of them.

Levente

On Wed, 4 Jul 2018, H. Hirzel wrote:

> Hello
>
> The installation of Metacello causes a VM crash.
>
> http://wiki.squeak.org/squeak/6157
> https://github.com/Metacello/metacello
>
>
> "Get the Metacello configuration (for Squeak users)"
> Installer gemsource
>    project: 'metacello';
>    addPackage: 'ConfigurationOfMetacello';
>    install.
>
>
> "Result : OK"
>
>
>
> "Bootstrap Metacello Preview, using mcz files (#'previewBootstrap'
> symbolic version"
> ((Smalltalk at: #ConfigurationOfMetacello) project
>  version: #'previewBootstrap') load.
>
> "Result : OK"
>
> "Load the Preview version of Metacello from GitHub"
> (Smalltalk at: #Metacello) new
>  configuration: 'MetacelloPreview';
>  version: #stable;
>  repository: 'github://Metacello/metacello:configuration';
>  load.
>
> "CRASH"
>
> "Now load latest version of Metacello"
> (Smalltalk at: #Metacello) new
>  baseline: 'Metacello';
>  repository: 'github://Metacello/metacello:master/repository';
>  get.
> (Smalltalk at: #Metacello) new
>  baseline: 'Metacello';
>  repository: 'github://Metacello/metacello:master/repository';
>  load.
>
>
> Regards
> Hannes