I have a database project in a solution which will not deploy from Visual Studio 2013. It fails with an error message "Unable to connect to target server". 
The same project, when opened in Visual Studio 2012 deploys without an issue.
The database is Sql 2012 hosted in a Sql 2014 engine (express)
The deployment settings are thus (with names changed to protect the innocent):
<?xml version="1.0" encoding="utf-8"?>
<Project ToolsVersion="12.0" xmlns="http://schemas.microsoft.com/developer/msbuild/2003">
  <PropertyGroup>
    <IncludeCompositeObjects>True</IncludeCompositeObjects>
    <TargetDatabaseName>TestDatabase</TargetDatabaseName>
    <DeployScriptFileName>TestDatabase.Database.sql</DeployScriptFileName>
    <TargetConnectionString>Data Source=.\SQL2014;Integrated Security=True;Pooling=False</TargetConnectionString>
    <ProfileVersionNumber>1</ProfileVersionNumber>
  </PropertyGroup>
</Project>
I have also tried the deployment with using a username and password rather than Integrated security...
 
    
 
     
    