Check your connection string. If you need help with it check Connection Strings, which has a list of commonly used ones.

Commonly used Connection Strings:

SQL Server 2012

Standard Security

Server=myServerAddress;Database=myDataBase;User Id=myUsername;Password=myPassword;

Trusted Connection

Server=myServerAddress;Database=myDataBase;Trusted_Connection=True;

Connection to a SQL Server instance

The server/instance name syntax used in the server option is the same for all SQL Server connection strings.

Server=myServerName\myInstanceName;Database=myDataBase;User Id=myUsername; Password=myPassword;

SQL Server 2005

Standard Security

Server=myServerAddress;Database=myDataBase;User Id=myUsername;Password=myPassword;

Trusted Connection

Server=myServerAddress;Database=myDataBase;Trusted_Connection=True;

Connection to a SQL Server instance

The server/instance name syntax used in the server option is the same for all SQL Server connection strings.

Server=myServerName\myInstanceName;Database=myDataBase;User Id=myUsername;Password=myPassword;

MySQL

Standard

Server=myServerAddress;Database=myDataBase;Uid=myUsername;Pwd=myPassword;

Specifying TCP port

Server=myServerAddress;Port=1234;Database=myDataBase;Uid=myUsername;Pwd=myPassword;

Oracle

Using TNS

Data Source=TORCL;User Id=myUsername;Password=myPassword;

Using integrated security

Data Source=TORCL;Integrated Security=SSPI;

Using ODP.NET without tnsnames.ora

Data Source=(DESCRIPTION=(ADDRESS_LIST=(ADDRESS=(PROTOCOL=TCP)(HOST=MyHost)(PORT=MyPort)))(CONNECT_DATA=(SERVER=DEDICATED)(SERVICE_NAME=MyOracleSID)));User Id=myUsername;Password=myPassword;