Just to add to the sense of mystery and awe, I record that booting to another, completely independent installation of 7.5.5 (or even 7.6.1) on an external drive, and then opening AppleShare from the System Folder of the problem installation of 7.5.5 on the CC's internal drive, works perfectly. A full panel of printer icons on the left (and AppleShare, of course), and effective communication and mounting of the drive alias from a remote drive or volumes. No sign of 'Quantum 250MB', the real one of which continues to sleep happily in the unconnected Classic.

Truly, in this case, Diabolus ex machina.

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