AdSense shows a blank space

I created an AdSense account a few days ago. But when I integrated it into my website, it only showed a blank space where I put the code without any contents. I googled the web and did not find a solution. Looks like not too many people have this problem, in case you get the same problem, here are some possible reason and solutions.

Reason 1: When you create an Ad unit, you choose to show a solid color when AdSense cannot find a match content on the page. And the solid color you picked is the same as the background color on the problem area.  
Solution 1: Most of time this is not a case. If it does, then try to used a different solid color.

Reason 2: You just created/updated an Ad unit, which usually take up to 10 minute to load
Solution 2: Wait 10 minutes to see it works or not

Reason 3: The AdSense code does not correctly paste. You cannot write the code in a single line.
Solution 3:

The is happen to me, see the code below,

//a sinlge line below causes a problem
<script type="text/javascript"><!-- google_ad_client = "pub-xxx"; /* 160x600, created 3/4/09 */ google_ad_slot = "9031182928"; google_ad_width = 160; google_ad_height = 600; //--> </script> 

After changed it like below, it fixed the problem.

<script type="text/javascript"><!-- 
google_ad_client = "pub-xxx";
 /* 160x600, created 3/4/09 */
 google_ad_slot = "9031182928";
 google_ad_width = 160; 
 google_ad_height = 600;
 //--> 
 </script>