Listbox problem selectedindex C#

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C#

Now I have a listbox I need to add in it name of day and time and the program read each item in listbox auto and if the first item = my pc day and time show message and so on... But I got dat error when the program reach the last item give me that error And when I click on start button it doesnot wait until the first item = my pc day and time it go on the each item until reach the last give me that error
note: The User WIll add items from 2 textbox then click on button the item will appear in listbox so i need the program read each item in listbox and if the day and time = pc day ant time show message

Error photo :
http://i.stack.imgur.com/77wZM.png[^]


in button add items to listbox code:

Listbox5.items.add(textbox1.text + textbox2.text)
Listbox5.selectedindex=0

in Button1 start timer code:

timer1.enabled=true;

in Timer1 code:

if (listbox5.text= datetime.now.tostring("ddd") +datetime.now.tolongtime())
 Messagebox.show("done")
 Listbox.selectedindex +=1

What I have tried:

iam tried the above codes. but i got error help?