I have a program working in the Android Emulator. Every now and again I have been creating a signed .apk and exporting it to my HTC Desire to test. It has all been fine.
for me the cause was that i had multiple builds using different build variants on same phone:
what happened was that some of these builds were built by me, another one was sent to me by another developer.. trying to install the developers while i had other builds (built by me) caused the above error.
so the fix was simple: delete all the builds on my phone (regardless of build variant).. then install the apk sent by my peer.. and it worked like a charm