Probably you are using the RadGrid in a scenario, which does not support modal popup edit form in IE. Such scenarios include placing the RadGrid inside a scrollable and/or positioned containers, or using grouping and static headers at the same time. If this is your scenario, increasing the popup z-index will unfortunately not help and you will have to turn off the modality. The problem is in the different way browsers implement z-index and stacking contexts. Sorry about the inconvenience.
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