Usually in the case of the bit flip the ace will reset itself, which clears the problem. In order to understand what is happining to your ACE, you would have to open a TAC case, and provide show tech information, as well as any files that were generated in the "core:" directory. You can view these using the command "dir core:"
It seems odd that the standby ACE also wouldn't respond to any command input. Did you have to reset it as well? If you had to reset it as well, then it may have encountered the same conditions that caused the hang on the primary.
Was there any syslog messages generated on the 6500 switch during the time?