ENABLING & DISABLING APPLET BUTTONS:

If it is form applet  then create new controls in controls...tools  >> applet>>control

Please check the Mode in which you have inserted the buttons. It must be Edit or Editlist. You may use PreCanInvoke and CanInvoke method to enable the buttons in script.

 We can also enable a button without script '(without using PreCanInvoke).  Prefix 'EventMethod' with the method name you want.ex: Method Name : "GetNextOrder".   For this control specify the method name as "EventMethodGetNextOrder".
         
This is useful only if button should be enabled without any condition.If you want to enable the button based on some condition then you have 2 implement the same using PreCanInvoke script only.

In Siebel 8, the buttons can be enabled/disabled using Applet User
Properties

            Name: CanInvokeMethod: MethodName
            Value: TRUE or using an Expression which results in TRUE/FALSE

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