Anil Kumar
How to set retry times for a particular request in crawl spider?
btw is that site uses any ajax/.Net/ViewState when you paginating? Maybe it shows error cause you have not filled some tokens/fields/parameters, I saw site before, which was allowed paginating only without concurrency, filling some tokens from previos request.
Also, you can show code + site, maybe somebody will take time to look at it little bit closer.