I succesfully updated Minecraft to the 1.9 version and was able to play it normally for a few days... then, today that I was trying to log in I got the following message:

"Error: no se ha encontrado o cargado la clase principal net.minecraft.client.main.Main
Java HotSpot(TM) 64-Bit Server VM warning: Using incremental CMS is deprecated and will likely be removed in a future release"

Once I saw this I hit again the Play button and an older version of the game was uploaded instead (1.8.9). I closed everything and started all over again and I noticed that it starts updating all the files just as if it were not updated already, but in the end I got the same error message... I also tried to restart the computer to no avail.

Any suggestions?