Bdw where did u get the Multiwii 2.5 from??? And from when are u using it ? Did u crashed while flying?

Nope its not connected to Multiwii Gui.
I bought it from rcmumbai. I just know its a FTDI Tool V1.0 ( that's what the chip says)

If you have a usbasp you can connect it to the isp and program it
Or if somebody.is.up for making an hex file just burn it to the board and you will.be good to go

For your problem there can be many reasons......
First of all you might be having wrong drivers for your USB to serial converter - if you post a close up picture of your ftdi tool or just post the number of the controller IC, we can help you with the correct driver.

If you have something else connected to the serial pins on multiwii board it can't be reflashed through UART pins. If you don't understand what I am talking about, then here is easy way - remove everything else from your multiwii board except the ftdi tool. !

Now let's assume the multiwii board is ready for programming and I the correct drivers for your ftdi is installed. You can check the connected port from device manager.

Now open arduino IDE , select Board  - Arduino UNO , port - the port for ftdi tool as seen in device manager ,  and programmer - AVRISP mk-II .

if you are using latest ftdi drivers then it won't work because company has started to brick duplicate ftdi chips because of chinese copy of arduino

also tell your chip number and if possible post a screenshot of your device manager

if you are facing the same problem as i did then i can help you

most probably its a driver issue

i saw your ftdi tool (its almost same as mine)

also fdti driver installs 2 drivers

1. usb serial port (which i can see in your screenshot com14)

2. usb serial converter ,which is present at the end of universal serial bus controller (which i am unable to see in your screenshot (scroll down ))

if these two are installed then your ftdi should work fine

if not then try these drivers CDM v2.12.00 WHQL Certified (there's a trick or way to install these which i can tell you after confirming its driver problem)

Okay if you say so, I'll give that a try, is that the lastest drivers or the older version of it ?
My FTDI is v1.0 chip.
N everything I tried had failed earlier ....

Older version

you didn't tell me if usb serial converter is installed or not

Yep both of the drivers are installed but the problem is that i have installed the latest from their site, i dn't knw which one's latest acc. to them ...

Your error message here clearly shows you do not have the driver for the board... Download the drivers from the below link and run it...You will now be able to detect the board
http://www.ftdichip.com/FTDrivers.htm

I do have the latest drivers CDM 2.12 or something ...
It doesn't works at all ...

Try uninstalling and then reinstalling from the site mentioned above

I have tried uninstalling, re installing ...
but the problem remains the same ...
I did exactly what i was told to do or what i have learnt from the internet but this thing doesn't works at all ....
many people have suffered through this but still haven't got any clear solution for this !!

can anybody tell me how to power multiwii with just a lipo n nothing else plugged in ?