I was trying to change my default/main/startup (whatever you call it) activity by editing the androidmanifest.xml file. All i did was change the android:name property. however, this completely broke the entire app. when i try to install it fails and reads
Installation error: INSTALL_PARSE_FAILED_NO_CERTIFICATES
when i tried to change it back to its previous state, it was still giving me the same error... what have i done!?!?!
Did you edit the AndroidManifest.xml directly in the .apk file? If so, that won't work.
Every Android .apk needs to be signed if it is going to be installed on a phone, even if you're not installing through the Market. The development tools work round this by signing with a development certificate but the .apk is still signed.
One use of this is so a device can tell if an .apk is a valid upgrade for an installed application, since if it is the Certificates will be the same.
So if you make any changes to your app at all you'll need to rebuild the .apk so it gets signed properly.