Assume that the Filter By Grid feature is enabled on the sales order grid in the Sales order dialog box in Microsoft Dynamics AX 2009. When you create a new record in the sales order grid, the leave event is unexpectedly triggered. Therefore, the focus is lost from the control.
Sometime the user gets error while typing item number because before typing the complete item number the leave event of the control gets triggered and so does the validate method of item Id. As the item number is not completely typed, the system tries to validate the incomplete item id and throws error.
Resolution to this error is given in Kernel Rollup 4 for Dynamics AX 2009 sp1. Upgrade your kernel roll up to 4th version.