MultiSendcon service won’t start after upgrading — "ChilkatDotNet47.dll or one of its dependencies could not be found"

After upgrading MultiSendcon from an older version (e.g. a 2021-era release) to the current version, the service fails to start. The internals.log file shows an entry like this:

Unhandled Exception:
The file or assembly "ChilkatDotNet47.dll" or one of its dependencies could not be found.
The specified module could not be found.

   at MultiSendconService.MSCService.UnlockChilkat()
   at MultiSendconService.Program.Main()

(On a German system the message reads: „Die Datei oder Assembly ChilkatDotNet47.dll oder eine Abhängigkeit davon wurde nicht gefunden.“)

Cause

The key phrase is "or one of its dependencies". The ChilkatDotNet47.dll file itself is present in the MultiSendcon program folder — what is missing is a dependency of it. Current versions of MultiSendcon use an updated Chilkat component that is built against the Microsoft Visual C++ 2015–2022 Redistributable (x64) runtime. Older versions used an older Chilkat build that relied on an earlier runtime, which was already installed on the server. After upgrading, the newer runtime is required but is not yet present, so the service cannot load the Chilkat library and stops within a few seconds of starting.

Solution

Download the latest Microsoft Visual C++ Redistributable (x64) directly from Microsoft. On the Microsoft download page this is the top entry, "Latest supported v14 (for Visual Studio 2017–2022)" → Latest supported Redistributable version. Choose the X64 build (vc_redist.x64.exe) — not x86 or ARM64.
Run vc_redist.x64.exe and complete the installation.
Start the MultiSendcon service again, either from the Windows Services console or from a command prompt:
```
sc start MultiSendconService
```

No reinstall of MultiSendcon is required. Once the runtime is present, the Chilkat component loads and the service starts normally. You can confirm success in internals.log — you should see the "Waiting for SMTP connections on …, IP port 2500" line instead of the exception.

How to verify it was the runtime: on the affected server, open a command prompt and run where vcruntime140_1.dll. If the file is reported as not found, the Visual C++ runtime was indeed missing — older redistributables (2013 and earlier) do not include this file, which the current Chilkat component requires.

For configuring the Exchange send connector that routes mail to MultiSendcon on port 2500, see How to manually create the MultiSendcon Send Connector in Exchange.