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You get an error similar to the following when browsing the Device Type page in SiteAdmin or when saving an Application in SiteAdmin
"Server Error in '/GpsGateServer' Application.
Operation is not valid due to the current state of the object.
This error occurs because of the amount of form fields that your device type contains. A limit of 1000 form fields was added in an ASP.NET security fix recently released by Microsoft.
See here for more info about the security fix: http://weblogs.asp.net/scottgu/archive/2011/12/28/asp-net-security-update-shipping-thursday-dec-29th.aspx
You can raise the limit by adding an application setting in the GpsGateServer/IIS/Web.config file.
<add key="aspnet:MaxHttpCollectionKeys" value="5000"/>