"Could not load file or assembly or one of its dependencies" in Mono but not in native .NET - mono

Question

The same executable that uses some proprietary DLLs, after being compiled with Mono, works natively on Windows, but doesn't work using Mono on Windows or Linux.
hello_onbase.cs:
using Hyland.Unity;
using Hyland.Types;
using System;
public class HelloOnBase
{
public static void Main(string[] args)
{
var auth = Application.CreateOnBaseAuthenticationProperties("app_server_url", "user", "password", "data_source");
var app = Application.Connect(auth);
Console.WriteLine ("OnBase connection successful!");
}
}
Proprietary DLLs Hyland.Unity.dll and Hyland.Types.dll are in the same directory as the file hello_onbase.cs. Unfortunately I can't share those files since they're the IP of our vendor, I'm very sorry...
I opened Mono x64 Command Prompt in Windows and compiled the file successfully with Mono:
C:\Users\apanasenco\git\docaccess\services\doc\onbase>csc -r:Hyland.Types.dll -r:Hyland.Unity.dll hello_onbase.cs
Microsoft (R) Visual C# Compiler version 3.6.0-4.20224.5 (ec77c100)
Copyright (C) Microsoft Corporation. All rights reserved.
The executable Mono compiled executes just fine natively in Windows:
C:\Users\apanasenco\git\docaccess\services\doc\onbase>hello_onbase.exe
OnBase connection successful!
However, running the executable with mono causes the following error:
C:\Users\apanasenco\git\docaccess\services\doc\onbase>mono hello_onbase.exe
Unhandled Exception:
System.TypeLoadException: Could not set up parent class, due to: Could not set up parent class, due to: Could not load type of field 'Hyland.Types.EncryptedServiceObject:_scp' (2) due to: Could not load file or assembly 'Hyland.Security.Legacy, Version=0.2.2.0, Culture=neutral, PublicKeyToken=e169a6a902bdd7a6' or one of its dependencies. assembly:C:\Users\apanasenco\git\docaccess\services\doc\onbase\Hyland.Types.dll type:EncryptedServiceObject member:(null) assembly:C:\Users\apanasenco\git\docaccess\services\doc\onbase\Hyland.Types.dll type:ParameterizedObject member:(null)
at Hyland.Unity.OnBaseAuthenticationProperties.ConnectNormalMode (Hyland.Unity.Services.IConnectServiceAccess connectServiceAccess) [0x00000] in <80532c8c2f134d0daba2ee8243cb5721>:0
at Hyland.Unity.OnBaseAuthenticationProperties.ConnectAndGetIntegrationApplicationOptions (Hyland.Unity.Services.IConnectServiceAccess connectServiceAccess) [0x00020] in <80532c8c2f134d0daba2ee8243cb5721>:0
at Hyland.Unity.Application.Connect (Hyland.Unity.AuthenticationProperties connectProperties) [0x00020] in <80532c8c2f134d0daba2ee8243cb5721>:0
at HelloOnBase.Main (System.String[] args) [0x0001b] in <73b1617068fa44e792f55cccc5974b17>:0
[ERROR] FATAL UNHANDLED EXCEPTION: System.TypeLoadException: Could not set up parent class, due to: Could not set up parent class, due to: Could not load type of field 'Hyland.Types.EncryptedServiceObject:_scp' (2) due to: Could not load file or assembly 'Hyland.Security.Legacy, Version=0.2.2.0, Culture=neutral, PublicKeyToken=e169a6a902bdd7a6' or one of its dependencies. assembly:C:\Users\apanasenco\git\docaccess\services\doc\onbase\Hyland.Types.dll type:EncryptedServiceObject member:(null) assembly:C:\Users\apanasenco\git\docaccess\services\doc\onbase\Hyland.Types.dll type:ParameterizedObject member:(null)
at Hyland.Unity.OnBaseAuthenticationProperties.ConnectNormalMode (Hyland.Unity.Services.IConnectServiceAccess connectServiceAccess) [0x00000] in <80532c8c2f134d0daba2ee8243cb5721>:0
at Hyland.Unity.OnBaseAuthenticationProperties.ConnectAndGetIntegrationApplicationOptions (Hyland.Unity.Services.IConnectServiceAccess connectServiceAccess) [0x00020] in <80532c8c2f134d0daba2ee8243cb5721>:0
at Hyland.Unity.Application.Connect (Hyland.Unity.AuthenticationProperties connectProperties) [0x00020] in <80532c8c2f134d0daba2ee8243cb5721>:0
at HelloOnBase.Main (System.String[] args) [0x0001b] in <73b1617068fa44e792f55cccc5974b17>:0
Mono version on Windows and Linux: 6.12.0
The older versions of these two files used to work on Mono before... I'm wondering if there's some Mono setting I can tweak to relax some assembly checks to match native .NET behavior?

Answer 1

Turns out the vendor does provide a file Hyland.Security.Legacy.dll that was alluded to in the error message. Including that file resolved the issue.