Default [q] xperia z (c6602) stock ftf flashing drivers problem

Guys, I wanna apologize to all of you if this thread (or similiar) already exist, but I have just registered on this forum and I really need help. Here is the thing;
I am from Croatia, little country in Europe, and I have Xperia Z C6602 with Arabian firmware. I bought Xperia like 15 days ago and I didn't know that there is Arabic (1270-7937) firmware on it. Now, i want to change firmware to Belgian (1270-6704) or US (1271-0119), or Indian at least (1270-7186) because i want to get updates quickly, and I was trying to flash it with flashtool. I downloaded firmware that I want, installed flashtool and drivers and tryed to flash it, and then i got this error: "DRIVERS NEED TO BE INSTALLED FOR CONNECTED DEVICE." The problem is that i have allready installed the drivers, and I was trying with reinstalling them or reinstalling flashtool, but i got this error every time.
Please, if anyone knows what is the problem, or if anyone can help me, write it here or send me a private message.
Once again, sorry for the tread (if it is stupid or nooby), but I really need help.
AND SORRY FOR MY BAD ENGLISH TOO :P