The current build operation (build key Build Key[Microsoft.Practices.EnterpriseLibrary.Data.Database, null]) failed: The value can not be null or an e

when you have implemented MS Enterprises Library then you face this error...

The current build operation (build key Build Key Microsoft.Practices.EnterpriseLibrary.Data.Database, null]) failed: The value can
not be null or an empty string. (Strategy type ConfiguredObjectStrategy, index 2)

so for this please add Default Databse in web.config

please ref Image for the solution