Internet Explorer 8 has a text box data entry problem known as “textbox inside an updatepanel with AsyncPostBack = unselectable textbox”. When page content is wrapped in an UpdatePanel and has multiple text boxes which have the AutoPostBack property set to ‘True’, then tabbing from one text box to another after entering data in the first text box results in the second text box becoming uneditable. After the postback is fired on the first text box, focus moves not to the next text box (even though the cursor is in the second text box) but to the address line. I.e., the page looses focus altogether. This does not happen in any other browser, including IE6, IE7 or in IE8 running in compatibility mode.
If you need to use UpdatePanel and PostBack, then force IE8 to start in compatibility mode by adding this tag to the master page’s <head> area:
<meta http-equiv="X-UA-Compatible" content="IE=EmulateIE7" />
Step 1: In Application Explorer, select the default master page (i.e. HorizontalMenu, VerticalMenu, etc.).
Step 2: In Design Mode, open the Page Directives dialog (right click, Page Directives…)
Step 3: Add this tag right after <meta> tag keywords.
Internet Explorer Browser Compatibility