Here is the solution to try
Nokia 5800 certificate expired error when you try to install applications it is expected that in the next firmware update for the Nokia 5800.
If you have already tried the solutions as
1. re-set the date of the phone for a few months ago,
2. allow installation of software for all your program manager,
3. Turn on the confirmation certificate online
4. or re-format the phone, etc., in this case is not everything for you, try the solution below - it works!
How to fix the Nokia 5800 "certificate expired" error during installation:
1) Backup all your messages, contacts, notes, calendar entries, etc. with the help of Nokia PC Suite.
2) After the backup, you have to remove the microSD card. Do not remove the card directly, when the phone is switched on, the card and the data can be corrupted. Proceed as follows to the microSD card.
a) Press the power key, sroll down and select "Remove memory card" option.
b) Click "Yes" when asked to "remove the memory card will close all open applications. Remove anyway?"
c) Shortly after the "remove the memory card and press OK" appears, the microSD to be separated from the slot and is now dedicated.
3) Enter * # 7370 #-code on the screen to your phone to factory settings. These are all your personal data.
4) Then the phone lock code if it has not changed, before they enter a default value is 12345.
5) The phone will reboot, choose your country as "US". Some users have reported that the phone works fine, even if the selection of his country, but only some US works. In US the best choice here by now, we can later.
6) Turn the phone over and over again to the Micro SD card slot in your memmory in 5800.
7) Restart the phone and it work! The Nokia 5800 is ready to any application you signed.
Nokia 5800 Xpress Music NEW v.30.0.011 firmware
Step 1: Go To Your Device Updates Menu
Activate your dial pad and press *#0000#
Step 2: Check for Updates 
Press Options, and select Check for updates.
Step 3: Start The Update
Select Now when you see the Software update downloaded from Nokia. Install now? pop up. Nokia’s device update will download the update using your device’s default access point. I have set mine to using my home’s wifi.
Step 4: Wait for Your Device to Update
You will see a white screen with a blue update bar. Do not panic, this is normal.
Step 5: Your Are Done!
Your device will automatically restart. Your new firmware would have been installed once your device has been rebooted. You should now have the firmware v.30.0.011 on your Nokia 5800 Xpress Music.
