Whatever you do, don't preload Mass Effect 3 from Amazon.
Wait for Amazon to give you your product key and preload directly from Origin. If you preload from Amazon, Origin has a hard time recognizing the install location and files because Amazon's preload file structure is different from the Origin preoload, so it makes you redownload the game with its own directory structure.
It's been a hassle to rework the Amazon directory structure into one that Origin recognizes.
**Update, I used the Amazon mass effect 3 product code in Origin and i have the option of downloading from Origin. For those who pre-ordered I have also redeemed my M55 Rifle via Origin. Now i have to find a way for Origin to recognize my Mass Effect 3 downloaded files(from Amazon).
To avoid any hassle, when you purchase this game on amazon just click on the link to redeem product code instead of download now. That what all you have to do is copy and paste that product code into Origin and you can start to preload from origin instead from amazon.
There is something wrong then because your game should be fully installed. No 99% or anything like that. You should have an icon on your desktop for Mass Effect 3 that when you try to start it bring up a authentication required message. Here are the steps I used to get the amazon download to load and install on origins.
Ok here are the steps if origin is giving you the can't install game error and wants you to redownload.
1. Have the download from amazon (around 10 gigs) 2. Try to install and get error (You will have redeemed your key and everything. You should now have Mass Effect 3 tied to your account). 3. Close Origin and go into your Program Files Folder (may be the x86 if you have 64bit) and locate the folder called Origin Games (ignore the one called Origin).** 4. Create a Folder called Mass Effect 3 inside Origin Games** 5. Open the amazon Mass effect 3 download folder (should have several files and folders, ignore them) and extract the "masseffect 3.zip" into the mass effect 3 folder you just created. The Mass Effect 3 folder inside of Origin Games should now contain several folders and files. 6. Relaunch Origins and it should have changed from needing to download to "ready to install"
** This step is different if you have changed where Origin installs your games at. For example I changed mine to install into a directory called Games in my C: Drive. If you did that then you create the Mass Effect 3 folder in whatever directory Origin is installing your games at and not in the Origin Games folder.
To get ME3 to install on my system I followed Jacob's steps above with one necessary change to step 5. I only copied the BIOGame folder (~9.7GB) from the extracted zip file to the 'Origin Games\Mass Effect 3' folder. Once copied I opened the Origin client and resumed the download. The download picked up at 97% and finished downloading the remaining ~300MB in about 5 minutes. Until I did this I continued to get the 'a problem occurred accessing the downloaded file' error at 99% complete.
I'm not certain but I think the cause of the 'a problem occurred accessing the downloaded file' error had something to do with the binaries folder from the Amazon zip not matching up with the binaries folder the Origin client was downloading. Again, just a guess on my part.
This was what finally worked for me. Copying the whole extracted zip file over overwrites something that Origin apparently needs, but just the one big folder will make it download a very little bit then install. All in all, you're better off just registering your key on Origin and letting it do the downloading itself.
OMG thank you. I have tried everything. I got "Your account is logged in on a different computer." "installation has failed." "Error 100: Try again later" and "problem accessing the download file" this finally worked!! I am so relieved.