exception in a button click event

Firstly, what is the value of index1? Why are you appearing to use it in conjuction with i to reference the same element of bu1? Are they in step?

Why are you using can_Count as your loop termination condition, but not checking that this is lower or equal to bu1.Length?

I am guessing that the error occurs on the line

bu1[index1] = new Button();

which would indicate the index1 is already outside the bound of bu1.

Put a breakpoint on the line

bu1[index1] = new Button();

Then run your program. Work out in your head what the various variables values should be, then check them. If they are ok, single step through repeating the checks until you spot the error. If they aren't what you think they should be, find out why not!

I suppose the problem is in bu1[ i ] - you use index1 in most places and then i in event handler attachment. i starts from 1, index1 most likely from 0. So you are actually trying to access next button which is not created yet.
Possible solutions:
1) use bu1[index1].Click += ...
2) bu1[i - 1 ].Click += .... (not sure about this one, depends on initial index1 value)

change this

bu1[index1].Click += new EventHandler(button1_Click);

In addition to other answers: your try-catch block makes no sense.

First, you probably think that you're catching some exceptions in this block if they are thrown in the handler. Hardly. You only try to catch exception on the operation of adding a handler to the invocation list of your event, which hardly would throw any exception.

More importantly, you're abusing exception mechanism by over-trying. Except for rare exclusions, you need to catch all exceptions in only one point of the code per thread. In case of UI, you need to catch them in a main cycle of UI. It could be event handler of the event System.Windows.Forms.Application.OnThreadException (Forms) or System.Windows.Application.DispatcherUnhandledException (WPF).

See:
http://msdn.microsoft.com/en-us/library/system.windows.forms.application.aspx[^],
http://msdn.microsoft.com/en-us/library/system.windows.application.aspx[^].

For more directions on use of exceptions, see my past answers:
How do i make a loop that will stop when a scrollbar reaches the bottom[^],
When i run an application an exception is caught how to handle this?[^],
throw . .then ... rethrowing[^].

—SA