The last available Geo Web Publisher SDK [geowebpublishersdk08111158en.exe] is suitable for commensurate and higher releases of Geo Web Publisher SS4 and SS5.
The 08.11.11.58 SDK relies on Visual Studio 2005 and is not easily migrated to later Visual Studio releases.
MicroSoft has discontinued support for Visual Studio 2005 as of April 2016: Support Ending for Visual Studio 2005
We therefore suggest that you obtain Visual Studio while still available.
As of this posting, Visual Studio 2005 and supporting packages can be obtained via my.visualstudio.com/downloads