To disable # call transfers:

• Login to the system administration
• Navigate to 'Extensions'
• Edit preferred Extension
• Click on 'Advanced Options'
• Remove 't' or 'T' from 'Incoming/Outgoing Dial Options'
• Click on 'Save'

NOTE: 
Some system applications also have their own dial options. If # transfer is to be disabled to all Queue calls, edit preferred Queue and remove 't' or 'T' from 'Incoming Options'.