Please make sure you have the most recent versions of DirectX and Microsoft .NET Framework installed on your system.

Microsoft .NET Framework can be found here:

http://www.microsoft.com/downloads/en/details.aspx?FamilyID=9cfb2d51-5ff4-4491-b0e5-b386f32c0992

The most recent DirectX can be found here:

http://www.microsoft.com/downloads/en/details.aspx?FamilyID=2da43d38-db71-4c1b-bc6a-9b6652cd92a3

If this does not resolve your issue:

1. Uninstall Stronghold Kingdoms from your system
2. Go to http://www.strongholdkingdoms.com
3. Login using your Stronghold Kingdoms login credentials
4. Download the Stronghold Kingdoms client and reinstall it