Flahtool bricked my phone

From last month I was trying to flash with different ftf's with flashtool
I was getting loader.sin error .
So someone one suggested me to use older version of flashtool .
So this time i've used flashtool-0.9.18.2 ..
and everything was going well ..
At the end of 90% + it came up with error ...
and this bricked my phone .

I want to know what's the reason of this problem and solution...
I need to downgrade from 5.1.1 .

(I'm repairing my phone with sony pc companion ... Help me with falshtool error fix )
:crying: