I had the same problem as the OP but it's easily solved.
If I go to the download page (
http://tasker.dinglisch.net/
download.html) in the Chrome browser on my Galaxy Nexus, and click the
download link for 1.2u2, it will download a file called Tasker.zip. If
I do the same in the stock browser, it will download Tasker.1.2u2.apk.
I presume the OP is also using a browser other than stock.
Solution is to download using the stock browser or rename Tasker.zip
to Tasker.apk but it's probably something you should be aware of
because most people wouldn't know why they are getting a .zip file or
what to do with it.
Cheers,
Daz.