Error - Invalid Object Name 'UserLock'

I am trying to execute a CREATE TABLE which results in the following SQL exception:

Invalid object name 'UserLock'.

The statement looks like this:

USE [db]
GO
CREATE TABLE [db].[dbo].[UserLock] (
[Login] [varchar](150) NOT NULL,
[ExpirationDate] [datetime] NOT NULL,
CONSTRAINT [PK_UserLock] PRIMARY KEY CLUSTERED
([Login] ASC)
WITH (PAD_INDEX = OFF, STATISTICS_NORECOMPUTE = OFF, IGNORE_DUP_KEY = OFF, ALLOW_ROW_LOCKS = ON, ALLOW_PAGE_LOCKS = ON) ON [PRIMARY]
) ON [PRIMARY]

The strange part is that I can run the query successfully inside the Microsoft SQL Management Studio with the same user but not within my .NET web application written in C#. I am not using any frameworks and I connect to the database with the provided classes out of System.Data.SqlClient. All other database queries work within the app. The database is Microsoft SQL Express 2005.

-- Edit ---

This is how my execution code looks like:

string createString = "CREATE TABLE [" + catalog + "].[dbo].[UserLock]("
+ " [Login] [varchar](150) NOT NULL,"
+ " [ExpirationDate] [datetime] NOT NULL,"
+ " CONSTRAINT [PK_UserLock] PRIMARY KEY CLUSTERED "
+ " ([Login] ASC)"
+ " WITH (PAD_INDEX = OFF, STATISTICS_NORECOMPUTE = OFF, IGNORE_DUP_KEY = OFF, ALLOW_ROW_LOCKS = ON, ALLOW_PAGE_LOCKS = ON) ON [PRIMARY]"
+ ") ON [PRIMARY]";
SqlCommand createCommand = connection.CreateCommand();
createCommand.Connection = connection;
createCommand.CommandText = createString;
selectCommand.ExecuteNonQuery();

I catch the exception in another method. The SQL connection itself is beeing set up in antoher method, aswell. It's the standard SqlConnection connection = new SqlConnection(connectionString);