On GemStone 3.3 and beyond, the hack of changeClassTo: to convert strings to UTF8 fails. Moreover, #_encodeAsUTF8intoString was added into the system so we should use that.

The new code should be:

GRUtf8CodecStream>>nextPutAll: 
  binary
    ifTrue: [ stream nextPutAll: aString asString ]
    ifFalse: [ stream nextPutAll: aString _encodeAsUTF8intoString ]

 Utf8>>asString
    ^ self decodeToUnicode

The whole discussion of this fix is in a thread "Again, Corrup Error preventing debugging real seaside exception" on the GLASS mailing list.

I am a bit out of time right now to setup everything to make a PR, but I will see if I have time later.