Cannot Access The File Because It Is Being Used By Another Process - Using ASPNETDB.MDF

I'm using Visual Web Developer 2005 Express, SQL Server 2005 and using the local file system as opposed to IIS for development purposes.

I will reference two pages of my site:  one that manages Types of Tours and one that downloads a Tour Registration Excel file.

On the Tour Types page, there is a sqldatasource that populates a DetailsView whose default mode is Insert.  On that same page I have a GridView that is populated from the same sqldatasource. The gridview has Paging, Editing and Deleting enabled.  There is no code behind on this page except for a prompt to the user to confirm the delete action if he has elected to delete a Tour Type.  This page works fine no problems.

On the download page, I have a prompt that allows the user to click a button to download the Tour Registration Excel file.  The code behind opens the Registration table in the ASPNETDB.mdf database, builds an .xls file via a streamwriter and prompts the user to download the file.

My problem:  if I start up VWD, go into my project, go straight to the download page without accessing any other pages, the download page works fine.  If I access any other pages first and then go to the download page, I get the error "System.Data.SqlClient.SqlException: Unable to open the physical file "C:....App_DataASPNETDB.MDF". Operating system error 32: "32(The process cannot access the file because it is being used by another process."  My simplified code behind is this:

Dim sw As System.IO.StreamWriter
Dim myConn As Data.SqlClient.SqlConnection, query As String, myCommand As Data.SqlClient.SqlCommand
Dim myReader As Data.SqlClient.SqlDataReader
Dim fileName As String, baseDirectory As String, fullFileName As String

fullFileName = baseDirectory & fileName
sw = New IO.StreamWriter(fullFileName)

myConn = New Data.SqlClient.SqlConnection("Persist Security Info=False;Integrated Security=true;AttachDbFileName=C:<pathnamehere>App_DataASPNETDB.mdf;database=ASPNET;Data Source=.SQLEXPRESS")

query = "SELECT Registrations.RegistrationNum, Registrations.Title, Registrations.LastName, Registrations.FirstName, Registrations.Organization, Registrations.StreetAddr1, Registrations.StreetAddr2, Registrations.City, Registrations.State, Registrations.Zip, Registrations.WorkPhone, Registrations.HomePhone, Registrations.CellPhone, Registrations.email, Registrations.AddToMailingList, Registrations.NumberInParty, Registrations.Comments, Registrations.DateRegistered, Registrations.TourDate, Registrations.TourFormattedTime, TourTypes.TourTypeDescr FROM Registrations INNER JOIN TourTypes ON Registrations.TourTypeNum = TourTypes.TourTypeNum"

myCommand = New Data.SqlClient.SqlCommand(query, myConn)
myConn.Open()

As soon as the code his the myConn.Open(), it abends with the above message.  I then have to close the project, and stop and re-start SQL Server.  HELP!!