"File downloaded is larger than expected" gamestop app mass effect download bug

Try disabling your antivirus / firewall.  Maybe also disable UAC.  

Diidn't work

Hm.  I don't know anything about the Gamestop app.  Do you install through it, Origin, or Steam?  (Or something else)  Is it possible to transfer the code?

Through impulse/gamestop application.

This is a tough one.  You're using the most recent version of Impluse?  

Reply #10 of this one might have some insight:

http://forums.wincustomize.com/371331/page/1/#2476902

This is three year old info, but:

Please do the following within Impulse:

-Click the blue menu button in the upper left
-Choose 'Preferences...'
-Click the 'Reset Data' button
-Close impulse and relaunch it. You may notice a long update time, which is normal as it is rebuilding the deleted info.

If this does not resolve the issue, try right clicking on ME and choosing, "download and archive." Once the archive is created, try clicking the blue button at the top left of Impulse and choosing "Restore archive."