Problems with flashing Xperia M2 D2303

Hello guys i had a problem with flashing my xperia casue i need back to stock - wanna my warranty back :D

Quote:

17/034/2015 19:34:30 - INFO - Selected Bundle for Sony Xperia M2 (D2303). FW release : 18.3.1.C.0.21. Customization : Play 17/034/2015 19:34:30 - INFO - Preparing files for flashing 17/035/2015 19:35:45 - INFO - Please connect your device into flashmode. 17/036/2015 19:36:13 - INFO - Opening device for R/W 17/036/2015 19:36:13 - ERROR - Drivers need to be installed for connected device. 17/036/2015 19:36:13 - ERROR - You can find them in the drivers folder of Flashtool. 17/036/2015 19:36:13 - INFO - Start Flashing 17/036/2015 19:36:13 - INFO - Processing loader.sin 17/036/2015 19:36:13 - INFO - Checking header 17/036/2015 19:36:14 - ERROR - Processing of loader.sin finished with errors. 17/036/2015 19:36:14 - INFO - Ending flash session

Info from Flashtool.
Actually i have 18.3.1.C.1.15 Z4-eXPERIance-lite .

Any ideas how to back to stock?