then check your disk for scratches.
md5 is a checksum thats created when all the data in the file is calculated. this number is generated on a per file basis. every file that is a copy of that main file will have the same md5 number and can only be changed if there is a change to the actual data. so something has corrupted the file.
a game patch can change the md5 but in that case the md5 number will get updated to the new file version if its a legitimate change.
so it has to be somewhere between coming off the disk to being installed on your hdd an error has occurred. if your running an unstable oc it can cause memory problems that would corrupt files. if your running cheat software this to can change the md5 numbers... also things like no dvd patches, but they tend to have there own md5 numbers.
have you tried scanning with another antivirus? avira is a good 1 and you can uninstall it when finished to carry on with the 1 you already have.
there aint many reasons to get this kind of error as you can see from the possiblitys mentioned above. so i would err on caution when you say its not a virus as you probably wont be using any of the other things that can cause it.
1 thing you can do is rename the install folder to duff or similar. and try reinstalling again. this will stop you writing to the part of the disk you have already used. if it installs properly then you may well have a HDD sector error.
i know you have already checked this but hdd scanners dont always pick up soft errors.
I have already copied the game disk as an image file in my hdd so scratches are not causing these MD5 error and i don't have any patch for this game yet. I did try to install the game in different drive but same problem occurred then i tried to install in XP as i am using 2 OS right now. So i think my OS is not corrupt.
Next i tried to install in my brother system but no luck here.
I think i should give a try to avast if you are recommending it.
Thanks for the reply by the way.
avira not avast.
you dont want the disk image you want the files from the disk image.
the easiest way to do it if its an iso is to use winrar.
just right click and extract to a folder of your choice then run setup or whatever to start the install.
if the iso is corrupt winrar will tell you pretty much straight away as this can cause an md5 error.