The database is looking for the log file in the directory specified in the mdf file, not where you placed it.

T-SQL

USE [master]

GO

CREATE DATABASE [AdventureWorks2012] ON

( FILENAME = N'<Enter path to the mdf file here>\AdventureWorks2012_Data.mdf' )

FOR ATTACH

GO

This will create a new ldf file in the default log file directory.

Management Studio

In the Attach Databases dialog box:

Click the Add button and browse to the mdf file

Click on the row that specifies the log file

Click the Remove button

Click OK