This is quite strange, so it's worth checking all the preconditions.
Please ensure that, before launching the Server, you followed the steps described in chapter 1.5 in
DOCS-SDKs\sdk_adapter_dotnet\doc\DotNet Adapters.pdf
which I resume below:

  1. The files in
    DOCS-SDKs\sdk_adapter_dotnet\examples\DotNetStockListDe mo\Deployment\Deployment_DotNet_Server(custom)\dot net_1.1
    make up the Remote Server and the mounted Remote Adapters. The Remote Server should be launched manually, through the
    DOCS-SDKs\sdk_adapter_dotnet\examples\DotNetStockListDe mo\Deployment\Deployment_DotNet_Server(custom)\Dot NetCustomServer.bat
    script.
  2. In order to communicate with the Remote Server, Lightstreamer Server should mount the so-called Proxy Adapter. This is accomplished by copying the contents of the
    DOCS-SDKs\sdk_adapter_dotnet\examples\DotNetStockListDe mo\Deployment\Deployment_LS
    directory in the Server's "adapters" subdirectory.
  3. The client should be modified in order to ask for data from the Proxy Adapter rather than from the preinstalled StockListDemo adapter. To make this step simpler, the Proxy Adapter is preconfigured with the same name as the preinstalled StockListDemo adapter, so that no changes on the client are needed. However, the preinstalled StockListDemo adapter must be removed, to avoid conflicts; hence the
    adapters\StockList
    directory should be removed.

Dario