Fix a bug in use of ENTER key in a ASP.NET grid of text boxes

I have an ASP.NET (c#) small application which uses a small SQL Server database. In this application, there is a data entry grid which is built dynamically in the c# code, made up of TextBoxes. Sort of forms a spread sheet for entry of data. Within the app, there is a line of code (shown below) which jumps to the next textbox depending on if the user presses the direction keys, or the ENTER button. When the focus moves to another textbox, it does come calculations, updates the value AND STYLE in some textboxes and then the UpdatePanel refreshes. So the problem is this, whilst everything works for the cursor keys, it does not work for the ENTER key. The use of the ENTER key updates the style of the grid (as it should) and does the calculations, but the updatepanel is not refreshed with the new TextBox values - even when I call the [login to view URL] in the background code. I need somebody who knows the way that textboxes deal with ENTER to find the cause and fix the bug. Will supply the SQL database (its small, and will be supplied in SQL 2008 backup), the VS2010 project (its small), and instructions. To do any entry which shows the bug is only about 40 key presses - its not a complex app, and the problem is very isolated. The line of the c# which deals with the Cursor (and ENTER) control is as follows: (note, variables are set with the UpBox, DownBox, RightBox and LeftBox TextBox names) cursorCOntrol = "var thisbox = [login to view URL](" + thisbox + "); if(event.keyCode==40 || event.keyCode==13 || event.keyCode==10) {var textbox = [login to view URL](" + downbox + "); [login to view URL](); } if(event.keyCode==38) {var textbox = [login to view URL](" + upbox + "); [login to view URL](); } if(event.keyCode==37) {var boxlen = textboxpos(" + thisbox + "); if(boxlen == 0) {var textbox = [login to view URL](" + leftbox + "); [login to view URL](); }} if(event.keyCode==39) {var boxlen = textboxlength(" + thisbox + "); boxpos = textboxpos(" + thisbox + "); if(boxpos >= boxlen) {var textbox = [login to view URL](" + rightbox + "); [login to view URL](); }}";