Can´t open version to play Minecraft

If I press on the "Play"-Button to launch any Minecraft-version, the Minecraft Launcher start to download the version I want to play once the loading strip reached the middle of the strip, the download stop and a window come out.
On this window is written "error😞"-----"The downloaded file could not be saved. 1.8.jar" (or other jar version if Iwant to play an another Minecraft version). If I press on the button below it ("Show more details") then it´s written that: "Name: 1.8.jar
URL: https://launcher.mojang.com/mc/game/1.8/client/d722504db9de2b47f46cc592b8528446272ae648/client.jar
Fehler-Details: Attempting to move successful download to C:/Users\Sebastien\AppData\Roaming\.minecraft\versions\1.8/1.8.jar Der Prozess kann nicht auf die Datei zugreifen, da sie von einem anderen Prozess verwendet wird
Dateiname: 383c-834e-7ad7-b2ec
Pfad: C:\Users\SEBAST~1\AppData\Local\Temp\383c-834e-7ad7-b2ec
Existiert: file" (I´m German so some words are there german)

Thanks in advance

Sébastien (ingame in Minecraft: Aracery)