Z3X Samsung Tool v.14.7 new version old bugs
 

It seems that i can use Z3x anymore for my work....Same bug on i9300:


Selected model: I9300
Selected port: COM3 Z3X BOX Serial Port
Selected port speed: 115200
Searching ADB device... OK
Reading phone info...
Model: GT-I9300
Android version: 4.1.2
Product code: Not Active
Phone version: I9300XXELLA
PDA version: I9300XXEMA1
CSC version: I9300ITVEMA1
IMEI: Unknown
Checking Super user right... true
Reading data from phone... OK
Repairing network settings... OK
Writing data to phone... OK
Rebooting phone... OK
Now connect phone to UART cable
Checking phone at COM3
Port open fail COM3
Done with Samsung Tool v.14.7
Done with Samsung Tool v.14.7

It seems that Z3X COM PORT is used by another application..
Remove and Re-insert z3x box,
try again..