Duplicate compilers detected

I just installed QtCreator on my new pc. On my old pc, everything was working well. 

I want to compile with gcc-8, so I create a new kit for that. When adding a compiler in the 'Compilers' tab, I get the error:

"Duplicate Compilers Detected"

"The following compiler was already configured:
GCC8
It was not configured again"

What I did:

Tools - Options - Kits - Compilers -> Add -> GCC -> C.
Name: GCC8.
Compiler path: /bin/gcc-8 (or /usr/bin/gcc-8)
Apply

And then I get this error.

Very annoying, since I can not compile my project now.