I have been using the command "Mosaic to new raster" so far successfully. Now, without changing any option from before, it just doesn't work anymore. It is something it already did: pretending to work, but actually gets stuck until I close it and open it again.
It doesn't fail, it is just still showing it is working, but it has already done after 1 minute. This time it didn't not work like that any longer. I closed the software and it just give me back standard "error".