HELP FOR -"App. closed Main Error"

It is most annoying n irritating error that might you are facing that time.......now you can solve that without formatting your phone....follow theses
1. First of all you will need any filemanager for that, like FExplorer, profiexplorer or ne thing.....if you don't have any filemanager right now, u can download one from my friend's blog:
http://chauhanmahesh.blogspot.com/2006/12/fexplorer.html
2. Open your filemanager or FExplorer..
3. Navigate to the folder "C:\System\Bootdata" and delete the file called "FirstBoot.dat"
4. Switch off your phone and then take the MMC out of it..
5. Swith on the phone again without the MMC, put the date and time data.
6. Now turn off the phone again.7. Insert the MMC in it..and switch on it again..

NOW THAT ERROR WILL NOT COMEE