This can be solved confirming following 2 points:
- Check whether you already have
System.Data.SqlServerCe
namespace added to
the References folder of your application. If its not there you
may right click the References folder and select Add references
option. From the popup window go to .Net tab and select
System.Data.SqlServerCe
from the list and click OK to add the namespace to the
project. - If you are OK with step 1, add
using System.Data.SqlServerCe;
to
the top of your code behind file which uses the
System.Data.SqlServerCe namespace.