When running EPiServer in .NET 4 you usually get the problem "A potentially dangerous Request.Form value was detected.."This can be solved by follow this guide: http://world.episerver.com/Articles/Items/EPiServer-CMS-60-now-supporting-ASPNET-40/
So far, so good. The problem is that I still have the problem when using the on page edit feature. The regular edit mode works fine. I have no idea why? Anyone else using the on page edit mode under .NET 4?
Are you sure a requestValidationMode attribute is not missing?