help with 'given path's format is not supported'

I have 5 HtmlInputControls on my webform allowing the user to upload 0-5 documents. I want the Upload button to upload the documents BUT NOT SAVE them yet. I don't want the SaveAs method to run until final submit of the form. So I have two methods to handle this. The second method, SaveFile( ), is not working. I get error message: The given path's format is not supported. I'm brand new to asp.net and don't have a great grasp of the different classes involved with the FileUpload so I'm not sure if I'm using them correctly. Would appreciated someone looking over my two methods.
 
protected void UploadBtn_Click(object sender, EventArgs e)
    {   //this method called when user clicks the Upload button of the HtmlFileInput control this method works fine
       
        /* get the files that are in the uploaded collection. If there are 5 HtmlInputControl ...