Newer versions of FlashTool sometimes drop support for very old phones (like the Xperia X10 or early Arc models).

Certain "one-click" root kits were built specifically to trigger off the architecture of version 0.6 series. Key Features of FlashTool

Click the "Lightning Bolt" icon, select "Flashmode," and choose your firmware.

Easily check the status of your bootloader or relock it if you need to return the device for warranty.