Hi Sherly,
Thank you for your interest in Syncfusion Products.
Internally our TextBoxExt is derived from TextBox. So to avoid returning to the newline of the TextBox by pressing Enter key when it is set to multiline we need to set the AcceptsReturn property of the TestBoxExt to false and need to set a button as the Form's AcceptButton. So when we press "Enter" key it triggers the default button's click event. Please refer to the below code snippet and the links for more details:
this.textBoxExt1.Multiline = true;
this.textBoxExt1.AcceptsReturn = false;
this.AcceptButton = this.button1;
http://social.msdn.microsoft.com/Forums/en-US/vbgeneral/thread/21977fb2-4c40-4223-8e7d-c3239e4e8f44/http://msdn.microsoft.com/en-us/library/system.windows.forms.textbox.acceptsreturn.aspxPlease let me know if any concerns.
Regards,
Fathima