ASP.NET 4.0 project dll not working in asp.net 2.0 project when mouse over on gridview not open popup

Question

I have Create one project in asp.net 4.0 and it's dll used in asp.net 2.0 project. work every thing fine but popup page open in gridview mouseover it's not open.
individual asp.net 4.0 project work fine but when used dll in asp.net 2.0 project it's not open popup page. any one have idea regarding this ?