Check the sql server connectivity. see machine.config for more details on connectionstring which is used for webparts

I think the best thing to do is make a web part containing the grid, then you can use Ajax to refresh the data. Hope this helps , Shirish.

You can either use javascript or requiredfield validatior for this

I think a usercontrol should be working totally independent (as per OOAD principles). However if you still want to do that you can raise event from usercontrol1 that gets handled in ASPx Page which will call the method from usercontrol2. I hope this helps. Shirish.