Your 9500/9500B communicates just fine over IEEE and then one day it doesn't.
There are a few reasons for this, one is when the emulation address is lower than the 9500B true address. Another is when the address is suddenly not recognized at all. Both situations can be solved by the following:
From the front panel of the 9500/9500B
Select Mode>Config then press More
Enter the default password (12321) or your unit's custom password.
Select the Bus Address key
First select the 5000 Series
Set the SG 5030 Emulation to address 19
Set the CG5011 Emulation to address 18
Save
Next disable 9500B emulation
This should result in the 9500B using address 18 and the other hidden mode using address 19. It is recommended the 9500B address be lower than the emulation mode address.
While here, check under the IEEE configuration menu for IDN?. There are settings in here that allow you to select how you want your 9500B to respond to the *idn? query that happens at the start of every MET/CAL procedure.
Very recent versions of MET/CAL won't work correctly unless the Manufacturer is set to "Fluke" and the model is set to "9500B".
Save
Power Cycle the 9500B
Set the mode to manual and try to connect again.