I had the exact same problem except our servers were running 6.1R2.0. I found that *some* of our servers would not accept the ESAP update when using Firefox, however in every case when I switched over to Internet Explorer 7 the update worked fine. Another thing to check is that you have no errors on your ethernets. I found that an IVE with ethernet errors will usually work fine for users (might be slow though), however it severely affect any software updates (firmware, ESAP, etc.) and they most often will fail.
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