Double-check the edmKey(s) in the app.config file in the AppHelper project, the connection string value might have been erased. The keys originally probably looked similar to this:
<edmKey connection="metadata=res://ServerModelNorthwindIB/ServerModelNorthwindIB.csdl|res://ServerModelNorthwindIB/ServerModelNorthwindIB.ssdl|res://ServerModelNorthwindIB/ServerModelNorthwindIB.msl;provider=System.Data.SqlClient;provider connection string="Data Source=.;Initial Catalog=NorthwindIB;Integrated Security=True;MultipleActiveResultSets=True""
containerName="ServerModelNorthwindIB.ServerModelNorthwindIBContext"
logTraceString="false" name="NorthwindIB" tag="">
<probeAssemblyNames>
<probeAssemblyName name="DomainModel" />
<probeAssemblyName name="ServerModelNorthwindIB" />
</probeAssemblyNames>
</edmKey>
<edmKey connection="metadata=res://ServerModelAw2000/ServerModelAw2000.csdl|res://ServerModelAw2000/ServerModelAw2000.ssdl|res://ServerModelAw2000/ServerModelAw2000.msl;provider=System.Data.SqlClient;provider connection string="Data Source=.;Initial Catalog=AdventureWorks2000;Integrated Security=True;MultipleActiveResultSets=True""
containerName="ServerModelAw2000.ServerModelAw2000Context"
logTraceString="false" name="Aw2000" tag="">
<probeAssemblyNames>
<probeAssemblyName name="DomainModel" />
<probeAssemblyName name="ServerModelAw2000" />
</probeAssemblyNames>
</edmKey>