Last day I made another attempt to upgrade the firmware of my Nokia 5800 XpressMusic to latest version that is 50.0.005. I was running version 40 before it. I read a lot on Internet that people are facing troubles after upgrading their phone software to this version.
I upgraded from OTA (on the air). I dialed *#0000# check for the latest updates. Connected it to the WI-FI Internet and upgraded it. I also face troubles when I upgrade my phone software last time. My phone keep on restarting after some time. At that time I keep my memory card inside. But this time I put my memory card out in this upgrade process. And there are no restarts till now.
So I suggest if you want to upgrade to this version, try this trick. Put your memory card out while downloading and installation.