error provider

Question

hi.....
I need to use error provider instead of messagebox.My problem is that when the user enter alphabets in the text box,the names starting with the alphabet should be displayed in the list box.So when there is no items in the list box starting with the alphabet entered by the user,i need to aler the user that "U should enter the names first in the table".I have used this code in the key up event of text box.
but when i used the error provider when the user enters the alphabet whose values are not in the database,the error is displayed.but when the textbox is blank,the provider is also there.Then how to hide the errorprovider???
please help me.....