HP 54710A User's Reference Manual page 166

Messages
A coupled control changed?
The question mark is a string substitution point that contains the name of a
control that changed, for example: A coupled control changed: Acquisition
Averaging. The message indicates that averaging was turned off because the
sampling mode was changed from equivalent time to real time.
A memory error was detected: Service is required
This is likely a hardware failure, although it could be a firmware error. It is
possible that you will lose data if you do not get the system serviced.
A system firmware file was not found on the disk
Either the file on the disk is corrupt or the disk may be the wrong one.
Acquisition is not possible on ?
This message is displayed as a reminder when a plug-in is installed in a
mainframe slot that has no acquisition hardware. For example, slots 3 and 4
of an HP 54710A or 54710D.
Busy timeout occurred with plug-in ?: Try reinstalling plug-in
The plug-in busy signal was present too long. The ? indicates which plug-in
had the timeout. Check the following:
Reinstall the plug-in.
Finger tighten the knurled screw on the front-panel of the plug-in.
If these actions do not solve the problem, there must be a hardware problem
in mainframe or plug-in. Call Hewlett-Packard service.
Caution: Do not exceed specified input rating on ?
Refer to the maximum input voltage rating on the front panel of the plug-in,
and reduce the size of the signal to within the allowable range.
Communication failure exists at slot ?: Service is required
There is a problem with the interface between the mainframe and the plug-in.
The ? indicates which slot has the failure. This is a mainframe hardware
problem if slot empty, otherwise there must be a hardware problem in
mainframe or plug-in. Call Hewlett-Packard service.
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