I'm seeing this during the ReleaseSqueakTrunk job:

ByteString(Object)>>doesNotUnderstand: #costume
[] in StandardScriptingSystem class>>removeUnreferencedPlayers
Array(SequenceableCollection)>>do:
StandardScriptingSystem class>>removeUnreferencedPlayers

StandardScriptingSystem class>>cleanUp:

But what's super entertaining about this is that the relevant method
looks like this (whitespace ruined thanks to Gmail):

removeUnreferencedPlayers
    "Remove existing but unreferenced player references"
    "StandardScriptingSystem removeUnreferencedPlayers"
    References keys do:
        [ : key | | ref |
        ref := References at: key.
        ((ref respondsTo: #costume) and: [ ref costume pasteUpMorph
isNil ]) ifTrue: [ References removeKey: key ] ]

So despite the #respondsTo: guard, a ByteString still gets into the
second block. Thoughts?

frank