Serial key fix (worked for me)

[Beinskalle]

Have a look at this, and read that long answer:

http://forums.steampowered.com/forums/showthread.php?t=2894940&page=2

[Sohei]

For convenience here is the suggested solution from that thread:

Originally posted by Steam Support:

-If you are running in Windows Vista or Windows 7, please completely exit Steam, and right-click on the shortcut which you use to launch Steam and select "Run as Administrator."

-If you are running in Windows XP, take the following steps:
1) Exit Steam.
2) Go to the "Start" menu, select "Run", type "regedit" and click "OK".
3) Navigate to the following registry key: HKEY_CURRENT_USER\SOFTWARE\VALVE
4) Right click and select "Permissions"
5) Check the boxes for "Admin" and "System" to "Full control" and "Read".

First, verify the GCF Cache for the game:
Title: Verifying GCF Cache Files
Link: http://support.steampowered.com/kb_a...2037-QEUH-3335

Verifying the GCF Cache solves most CD Key issues for most users.


If it still doesn't work, please try deleting your Mount & Blade registry entries:

Go to the "Start" menu, select "Run", type "regedit" and click "OK".

Navigate to the following registry key: HKEY_CURRENT_USER\Software\MountAndBladeKeys
Note: In 64-bit operating systems, this path may begin as: HKEY_LOCAL_MACHINE\SOFTWARE\Wow6432Node\

The data contents of the registry entry "serial_key" are your CD Key. Please write this down.

Right click on the registry value "serial_key" and select "Delete."

Exit regedit.

Load Steam.

From the Library list, right-click on "Mount & Blade" and select "Properties" from the menu.

Select the "Local files" tab and click the "Verify integrity of game cache..." button.

Steam will verify the game cache files (GCF's) - this process may take several minutes.

Once the process is completed, the "Check" window will automatically exit and you should be able to launch your game.

You may also try using the key previously found in your registry if M&B asks for a CD Key again.