SQL Server Database connection error with modules

Error:
DotNetNuke.Services.Exceptions.ModuleLoadException: A network-related or instance-specific error occurred while establishing a connection to SQL Server. 

Error Detail:
Error: UsersOnline is currently unavailable.
DotNetNuke.Services.Exceptions.ModuleLoadException: A network-related or instance-specific error occurred while establishing a connection to SQL Server. The server was not found or was not accessible. Verify that the instance name is correct and that SQL Server is configured to allow remote connections. (provider: SQL Network Interfaces, error: 26 - Error Locating Server/Instance Specified) ---> System.Data.SqlClient.SqlException: A network-related or instance-specific error occurred while establishing a connection to SQL Server. The server was not found or was not accessible. Verify that the instance name is correct and that SQL Server is configured to allow remote connections. (provider: SQL Network Interfaces, error: 26 - Error Locating Server/Instance Specified) at System.Data.SqlClient.SqlInternalConnection.OnError(SqlException exception, Boolean breakConnection) at System.Data.SqlClient.

Solution:
Make sure the connection string value under appSettings is the same as the connection string under the connectionStrings section.