Well, if it is still saying that, it didn't take then. I suggest doing the fix all over again (from the youtube explanation if need be- can be found on the nitdroidforums) and you should only need to reboot once. Try rebooting just once and then open market, close it, open it again, close it, etc. I did it 10 times I think before it actually worked. To properly close, you can download (hopefully) Task Killer, or some equivalent. It is an app that is run so you can kill any tasks you have. It's a downfall (a serious one at that) of Android that you need an app to kill other apps but it is what it is.

Once you stop seeing the "no matching content" in the market, then you should be alright to download astro. Someone else alluded to using the stock file manager but I'm not sure that would work, even in .apk format. Let us know if you have any more problems though.

Edit- link to the nitdroid forums with the youtube fix for anyone who wants a visual aid (it helped me.)
http://forum.nitdroid.com/index.php?topic=480.0