could be this.....

System Requirements
Supported Operating Systems: Windows 2000 Professional Edition ; Windows 2000 Server; Windows Server 2003; Windows Server 2003 Service Pack 1; Windows Server 2003, Enterprise x64 Edition; Windows Server 2003, Standard x64 Edition; Windows XP; Windows XP 64-bit; Windows XP Home Edition ; Windows XP Professional Edition ; Windows XP Service Pack 1; Windows XP Service Pack 2
PC with Pentium 400 MHz or faster processor; Pentium 800 MHz or faster recommended
96 MB of RAM (128 MB or higher recommended)
Microsoft Internet Information Services (IIS) 5.x or 6.0 and
One of the following is required:
Microsoft Visual Studio 2005
Microsoft .NET Framework SDK version 2.0

Note: IIS is not required when using SOAP messages with the TCP protocol.
Note: WSE 3.0 is not supported if installed on a computer with a version of the .NET Framework earlier than 2.0 or a version of Visual Studio earlier than Visual Studio 2005.