I tried to reproduce the problem in our local test by creating a simple page based on your given snippet code and bind WebGrid to OrderDetails table of Northwind database. My efforts were not successful – everything worked smoothly and the Review Changes popup window tooks less than three second to load.

I also made a test on our live sample that has its ‘AllowReviewChanges’ feature enabled at this following link, http://live.intersoftpt.com/cs/WebGrid/BatchUpdate_Enterprise.aspx?noframe=1, and found out that the ‘Review Changes’ popup window only takes less than four second to load.

I’m willing to advise you further but in order to do so we would need you to elaborate on your specific scenario and possibly give us a running simple sample that replicates the issue or a step-by-step guide that we can use to observe the problematic behavior.