After firmware upgrading my Sony Ericsson K800i I suddenly found myself unable to download Google Maps which was very annoying as its quite a neat feature.  The error code read “Invalid application”, and there was just nothing to do the errorcode came up every time not matter what..

it took a bit of debugging but the solution seemed to be in a post on the Google Maps Forum from a guy called Thorsten;

I think I found a solution (to be fair: I found the solution in another forum 🙂 !!

It might be done differently on other models but it worked on my SE K800I:

Within the menu, choose “Settings”. Go to the “Connectivity” tab and choose “Internet settings”. Select “Settings for Java” and choose “More” on whatever profile you are using. Go into the settings and change “Use proxy” to “No”. Now go to google.??/gmm, whatever suits you !!) and download the application.
My initial homepage did not work when entering the Internet but I was able to connect to anyway and download the application.  After downloading I went back to the settings and changed “Use Proxy” back to “Yes” and the homepage worked again. But more important …… Google Maps still works ….. Happy day 🙂