Why does the compiler behave like this?

Question

C++ / C#

Recently, the C# compiler has begun to delight to tears. Either the data disappears , now it does not see the assembly.
In the black frame is the project of the assembly itself.

The main thing when I write using AutoL and press Ctrl + Space is that he sees everything and completes it.
In another project (earlier), interestingly, everything builds and runs without any errors.
Solution: use the same version of the .NET Framework both in the assembly and in the project. I have a library on 4.5 and an application on 3.5
But still see my question about data loss during deserialization .

Answer 1

I had this with libraries. When one library is installed 2 times, for example under no 2.0 and 4.0. Or we have the same libraries with different names in the project. If you leave everything in 1 copy, and clean the rest, then the error disappears.
and about "4.5 and the application on 3.5" - these versions are practically not compatible. on the contrary, it might still work, but so - change everything for some one, otherwise it will be even worse further.