Error building Player: Extracting referenced dlls failed.

I added some DLLs to my assets/plugins folder and I use them in my code.

The code works fine and the DLLs work when I play the game inside the editor.

But as soon as I compile the build into a standalone version I get this error

Error building Player: Extracting referenced dlls failed.

anyone have an idea on how to fix that.

The DLLs are only compatible for windows, but that is ok because Its for a special purpose program that will only ever be run on a windows platform.

I am building it with the target platform being windows.

turns out Edit > Project Settings > Player > Optimization

change compatibility from ".net 2.0 subset" to ".net 2.0"

Very often if you're playing right before building, it'll lock the dlls, making it difficult to move them into the build.

If that happens, just relaunch unity and build again, without hitting play

Perfect!
Changing “.net 2.0 subset” to “.net 2.0” in Edit > Project Settings > Player > Optimization.

I have the same problem, I added the Database dll’s and it doesn’t build and say me the same error when I try to build.

I have set the compatibility to “.net 2.0” too

Perfect! Changing “.net 2.0 subset” to “.net 2.0” in Edit > Project Settings > Player > Optimization. but i’ve this error after
Error building Player: SystemException: ‘System.Net.Sockets’ are supported only with Unity Android Pro. Referenced from assembly ‘Mono.Data.Tds’.

Perfect solve, Change Play Setting: “.net 2.0 subset” => “.net 2.0”.

The Dlls you added are conflict with Unity inner Dlls. Because they have the same namespace.

He said is right!That’s not a problem anymore!