NsWebServices are not accessible when "Forms Authentication" is enabled in SIM
ITMS 8.7.x
The NSWebService calls were expected to be "internal" and not updated to Forms/Token authentication - that's why the default ASDK calls are working, but the particular ResourceModel.asmx from internal was failing with security response.
This issue has been fixed in our ITMS 8.8 Release
Meanwhile Workaround exists to manually change authentication for NSWebService web application from Forms to Windows. Assume that IIS restart must be performed after that.
NSWebService is an ASDK kind of web service, it appeared that it must not be switched to Forms authentication.