asp.net button focus problem

a simple [login to view URL] project (in c#, asp.net) is attached with the bid request. as you run the project, you will see two sets of buttons and text box. when you press "enter", always first submit button's code is being executed no matter which text box has focus. i need this to be changed in such a way so that submit button's code will be executed depending on which text box has focus. for example, if set 1's text box has focus, 1st submit button's handler will execute. if text box 2 has focus, 2nd will execute etc. thanks ## Deliverables 1) Complete and fully-functional working program(s) in executable form as well as complete source code of all work done. 2) Installation package that will install the software (in ready-to-run condition) on the platform(s) specified in this bid request. 3) Complete ownership and distribution copyrights to all work purchased. ## Platform asp.net c# windows