There is an incompatibility between HyperCard 1.2.5 and the Sound Manager in all system software beginning with System 6.0.6.
HyperCard 1.2.5 can run on 6.0.6/6.0.7 if the sound is set to 0 in the Control Panel before starting HyperCard. This incompatibility has been fixed in HyperCard 2.0.
This article is adapted from the Claris Tech Info database.