thank you,
i used this code & it fixed it:
'Add runtime management
ESRI.ArcGIS.RuntimeManager.Bind(ESRI.ArcGIS.ProductCode.Desktop)
'Initialize the application.
Dim licenseStatus As esriLicenseStatus = esriLicenseStatus.esriLicenseUnavailable
Dim m_AoInitialize As IAoInitialize = New AoInitializeClass()
licenseStatus = m_AoInitialize.Initialize(esriLicenseProductCode.esriLicenseProductCodeArcInfo)
licenseStatus = m_AoInitialize.CheckOutExtension(esriLicenseExtensionCode.esriLicenseExtensionCodeSpatialAnalyst)