An invalid checksum indicates that the file might have gotten corrupt during download. This typically happens on very slow or unreliable connections.
You could try downloading again and see if it works.
What computer/OS are you using?
You could also have a look at http://forums.adobe.com/thread/1006208. It has some more details why this error can occur and how to work around it.
I first tried downloading Premiere elements 10 on my new Macbook Pro
wirelessly. The download took close to 10 hours and then it wouldn't
extract after 15 hours. I then tried my older iMac with Snow Leopard which
is wired and it took 5 hours to download and wouldn't extract. Both
computers showed the 'invalid checksum" pop-up. I might have to phone my
If the download is completed in the Adobe Download Assistant you can temporarily turn off the feature to verify the checksum. The following steps will allow you to temporarily disable this feature:
I would recommend turning this feature back on though after the installation is complete. Also if you notice this happening on additional files it can indicate a problem with your Internet connection.
I phoned my internet provider and they upped my connection speed (for a
fee of course). I downloaded the Premiere Elements 10 trial version in
two hours or so and everything seems to be working properly.
Thanks for your time!