If you have validation controls and RadGrid in the same page, when you are trying to add a new record using the RadGrid Insert command the other control in the same form will fire validation. To solve this issue use this setting in your RadGrid
<ValidationSettings EnableValidation="false" CommandsToValidate="NO" ValidationGroup="no" />
Basically I am tricking the RadGrid control by passing bogus string to CommandToValidate and ValidationGroup in addition to EnabelValidation should be set to false.
I believe this a bug in telerik control but they claim fixed the issue.
I use version: 2009.3.1407.35