After an IOS 6.1 update my Ipad2 has crashed, all I get is file download that was corrupted message >

See Here > http://support.apple.com/kb/HT1808

You may need to try this More than Once...

Be sure to Follow ALL the Steps...

But... if the Device has been Modified... this will Not necessarily work.

I have an iPad 2 with 6.0.1 that I tried to update to 6.1. The process completely "bricked" my iPad. By reading this and a few other threads I deduced that the 6.1 update appears to be toxic for iPad 2s. It hasn't been fun, but I'm slowly getting back in action and this is how I did it (I'm on a Mac and I assume much of this will be similar for PC users):

1. I started by going to this web site to get the proper iOS file.http://www.felixbruns.de/iPod/firmware/ These updates are hardware specific and I had to experiement in downloading several until I found the correct one. Once downloaded from Safari I dragged the firmware files to my desktop.
2. I'm assuming that after failing to update your iPad that you'll see the "Connect to iTunes" on the screen. Go ahead and plug your iPad in and and iTunes should recognize it. You will then be asked to update and restore.
3. This is important: do not click the "update and restore" button. That will only repeat the download/firmware crash issue. Hold down the OPTION key and then click on update and restore. That will open a window that you can browse to the desktop where you put the firmware files. Choose the file you believe is the correct one for your iPad. I had to repeat this process 4 times, but when you do click on the correct version it will start the update process for the iPad.
4. Once the process is complete you should have 6.1 properly installed.
5. At this point you can restore from iCloud or your computer. Two years ago I switched to iCloud backup and I was frustrated that the message I got from the iPad was that there wasn't an iCloud iPad backup (which I have set up on all our iOS devices). :-( It's going to take a few hours to put everything right.

I've worked with Macs since 1985 and have to remind myself that software update problems like this one used to occur a lot more regularly. We've all gotten used to a much more stable software environment, but that's only a mild comfort for losing about 5 hours out of your day.