New Post: User.GetUserFromId

Ok well firstly if your method doesn't return a value it should be set as void eg

  public void GetImageUrl(string providerUserID)

{
    try
    {
        var user = User.GetUserFromId(long.Parse(providerUserID));

        if (user != null)
        {
            return user.ProfileImageUrl;
        }
    }
    catch (Exception ex)
    {
    }
}

}

1. Is the code to return the providerUserID functioning correctly? (Does it return a valid ID everytime?)
   
2. You could also try Convert.ToInt64() instead of long.Parse() - I believe they both return the same though so It may not matter.
   
3. The only reason I can think of what with what I've seen of your code is when you refresh the page the variable providerUserID is being unset on refresh.
   

Edit: Can't get it to format the code correctly but you want to remove "return null;" and replace "public string GetImageUrl(string providerUserID)" with " public void GetImageUrl(string providerUserID)" because you are not returning a string.