I got the same error loading BaselineOfMetacello, in this method... 
Could be an issue with github?

retryingResolvePackageSpecReferences: packageSpec gofer:

The error is Could not resolve: BaselineOfMetacello, with this spec:

spec
     name: 'BaselineOfMetacello';
     repository: 'github://Metacello/metacello:master/repository'.

The underlying repositoryError in 
MetacelloFetchingMCSpecLoader>>#retryingResolvePackageSpecReferences:gofer: 
is this: GoferRepositoryError: UndefinedObject>>isAlphaNumericThis error 
is reproducable after closing the error dialog and running again. Same 
issue.

k, r

On 3/27/20 11:43 AM, Fabio Niephaus wrote:
> Installer ensureRecentMetacello.

-- 
Kindly,
Robert