FileNotFoundException was unhandled

Could not load file or assembly 'System.Data.SqlServerCe, Version=9.0.242.0,
Culture=neutral, PublicKeyToken=89845dcd8080cc91' or one of its dependencies.
The system cannot find the file specified.

You might encountered this error when the System.Data.SqlServerCe version has redirected to another newer version due Visual Studio 2005 generated code on your application config file.

To solve this problem, you have to delete something like below in you app.config file.

xmlns="urn:schemas-microsoft-com:asm.v1">

name="System.Data.SqlServerCe" publicKeyToken="89845DCD8080CC91"
culture="neutral"/>
newVersion="9.0.242.0"/>

hope this helps