Since you don't save your CSV file during your open/close trick, my assumption is that the CSV file stays bitwise identical and therefore consequently is not the reason for your problem at all.

It looks more like one of these weird java issues (configuration, memory, etc)

You should try the same on a different computer or in a VM.

An other idea would be to check that the csv is not open (eg. by Excel) when you try it the first time. Open file handles my lead to trouble.

Instead of using dataloader cli you might also consider to have a look at TalenD: http://www.talend.com

Exception when Importing .csv file from CLI
The code I'm using is this one 

background: url(bilder/cover.jpg) no-repeat center center fixed; 
-webkit-background-size: cover;
-moz-background-size: cover;
-o-background-size: cover;
background-size: cover;
}


What I'd like to accomplish is that the background image is changed after like 2 sec to a background image that then stays put.

I know there are Jqueries for changing backgrounds like this but I'm not sure how to make something like that work with the code I'm using! It would be awesome if someone hade a solution to this!

My starting point for changing background was the code I found on w3schools:

{
width:100px;
height:100px;
background:red;
animation:myfirst 5s;
-webkit-animation:myfirst 5s; /* Safari and Chrome */
}

@keyframes myfirst
{
from {background:red;}
to {background:yellow;}
}

@-webkit-keyframes myfirst /* Safari and Chrome */
{
from {background:red;}
to {background:yellow;}
}

