Q:Could not load file or assembly 'System.Data.SqlServerCe, Version=4.0.0.0, Culture=neutral, PublicKeyToken=89845dcd8080cc91' or one of its dependencies

ANSWER:Generally you need to make sure you have updated any Project references to point to the 4.0 managed DLL which usually located at: C:\Program Files\Microsoft SQL Server Compact Edition\v4.0\Desktop (System.Data.SqlServerCe.dll). If your references are located in the application folder, then make sure all the dlls are copied and confirm the versions are the same. If the app.config file existed, check it . This file could redirect assembly references version at run time . Such like: 

<assemblyBinding xmlns="urnchemas-microsoft-com:asm.v1">

            <dependentAssembly>

                <assemblyIdentity name="System.Data.SqlServerCe" publicKeyToken="89845DCD8080CC91" culture="neutral"/>

                <bindingRedirect oldVersion="0.0.0.0-9.0.242.0" newVersion="4.0.0.0"/>

            </dependentAssembly>

        </assemblyBinding>

 

没有安装Microsoft SQL Server Compact.  EG:Microsoft SQL Server Compact 4.0 Setup

地址：C:\Program Files\Microsoft SQL Server Compact Edition

或者Compact 版本不对