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;

This might help someone.. My password contained a semicolon so was facing this issue.So added the password in quotes. It was really a silly mistake.

I changed the following :

<add name="db" connectionString="server=local;database=dbanme;user id=dbuser;password=pass;word" providerName="System.Data.SqlClient" />

to

<add name="db" connectionString="server=local;database=dbanme;user id=dbuser;password='pass;word'" providerName="System.Data.SqlClient" />

Set the project containing your DbContext class as the startup project.

I was getting this error while calling enable-migrations.Even if in the Package Manager Console I selected the right Default project, it was still looking at the web.config file of that startup project, where the connection string wasn't present.