Same problem ...
I am having the same issue of 0 mb phone memory. Unlike your case I wasn't even trying to upgrade/downgrade. From last few days I was getting "android.process.acore has stopped unexpectedly " and I have to force close it. After closing , the phone seems to be come unstable and unresponsive.
Now I am not able to install any application due to 0 mb problem, as well as each application run gives some sort of process unexepectedly stopped and force close error.
Was your problem solved ?
Is my internal card corrupted ?
Shall I upgrade to firmware or next version ?
Please guide me to the solution...
Thanks in advance !