Weird and persistent error : Microsoft (R) Visual C# Compiler version 3.5.0-dev-20359-01 (8da8ba0c)

I have this error in Unity:> Microsoft (R) Visual C# Compiler> version 3.5.0-dev-20359-01 (8da8ba0c)> Copyright (C) Microsoft Corporation.> All rights reserved. It appeared on a project that was perfectly working before. I simply deleted a little line in one of my scripts in Visual Studio (with no bug in it), then saved. Since then, the error occured, and I couldn't launch the project anymore, as "all compiler errors have to be fixed before you can enter playmode". The biggest problem is that not only the error persists in my project, but also in all the other projects! I even tried to uninstall/reinstall Unity, Visual Studio, Unity Hub, but it seems that now I'm stuck with this forever. I also deleted the project that triggered the bug. Does anyone have a single clue about this? I saw one or two people having the same problem on this website, and with no other solution than formatting the hard drive. As I'm not working on my personal computer, I can't do that...I mean, there must be a rational explanation to this bug!! Thanks you very much for your help.