I have a very wired error, one of my custom controls seems that is create two compiled files, and when I try to load it dynamically with LoadControl() is just f
After a lot of debug on a upgraded ASP.NET website, my last bug was this one on runtime.
I just checked the Build/Publish option "use fixed naming and single page assemblies" and it solved my case :)
Here some useful links: https://msdn.microsoft.com/en-us/library/hh475319(v=vs.110).aspx
https://msdn.microsoft.com/en-us/library/aa479044.aspx
http://forums.asp.net/t/960707.aspx