What does the following error message mean?!
ERROR(CMD441-TAD1-NAL85): OS has locked out debug during OS save restore.
The error message suggests that one or more of the processors on your target have powered down and the "OS Lock" and/or "OS Double Lock" feature that the OS uses to prevent the debugger from interfering with the power down sequence is preventing the DS-5 Debugger from connecting to the processor(s). This error message is more likely to occur if you are using an older DS-5 version and an older DSTREAM-ST/DSTREAM/RVI firmware version. The current DS-5 version is 5.27.1 and the current DSTREAM-ST/DSTREAM/RVI version is 4.31.0.
If you have tools support with Arm, I would recommend contacting the Arm Software Support team at support-sw@arm.com so they can investigate the message further.