I came across this error recently, on a website which I had built for one of our clients.
`Operation is not valid due to the current state of the object`.
This occurs on Postback of the page.
After a quick search, I found the answer on Stackoverflow
A security update for Microsoft .Net Framework meant that the number of fields which, by default, were allowed to be posted to a page was set to 1000, however the website in question was posting more. A quick fix for this is to add a setting into your web.config file;
<appSettings>
<add key="aspnet:MaxHttpCollectionKeys" value="2001" />
</appSettings>However, this forced me to realise how poorly coded this individual page was, and that I had been using far too many HiddenFields within DataGrids, GridViews and Repeaters.
On this problematic page, I was using HiddenFields to hold information for each item in the repeater control, and when the repeater was being Paged this worked fine. The client had asked for a facility to "View All", which meant that there were potentially 500 + items within the repeater, and each Item had 5 HiddenFields. I had never really thought about it before, but now I realise that there would be times when the page was posting 2500+ fields to the page!!! No No No.
I have updated the HiddenFields to Literals now and everything is working as it should, also I have cut the ViewState down massively!
This is just another reason though why I am glad to be moving away from webforms and the <form runat="server"> wrapping pages. MVC FTW!!! :)
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