A problem I've run into before is invalid line breaks that produces the same result. What I've done to "fix" this issue is to customize my AdSense code so that there are no line breaks.
Default AdSense Code:
<script type="text/javascript"><!--
google_ad_client = "pub-5538796211688403";
google_ad_width = 336;
google_ad_height = 280;
google_ad_format = "336x280_as";
google_ad_type = "text_image";
google_ad_channel ="";
//--></script>
<script type="text/javascript"
src="http://pagead2.googlesyndication.com/pagead/show_ads.js">
</script>
AdSense Code with no line breaks:
<script type="text/javascript">google_ad_client = "pub-5538796211688403";google_ad_width = 336;google_ad_height = 280;google_ad_format = "336x280_as";google_ad_type = "text_image";google_ad_channel ="";</script><script type="text/javascript" src="http://pagead2.googlesyndication.com/pagead/show_ads.js"></script>
The biggest thing to remember is to remove the comment code, highlighted in red below:
<script type="text/javascript">[b][color=CC0000]<!--[/color][/b]
google_ad_client = "pub-5538796211688403";
google_ad_width = 336;
google_ad_height = 280;
google_ad_format = "336x280_as";
google_ad_type = "text_image";
google_ad_channel ="";
[b][color=CC0000]//-->[/color][/b]</script>
<script type="text/javascript"
src="http://pagead2.googlesyndication.com/pagead/show_ads.js">
</script>
That took care of the "disappearing ads" for me.
Also, you shouldn't need to make any special changes to your robots.txt file. The default file has worked fine for me for over 3 years.
As far as whether AdSense is worth it or not....
Literally, books have been written on the subject, but here's my 30 second interpretation...
If you narrow your nitch down tightly enough
market your site effectively
drive enough trafic to your site (>500,000 unique visitors per mo)
Use relevant keywords in your META tags (must be relevant to the page content [not easy with XOOPS])
You can do well with AdSense. Personally, I make enough per year to cover all my hosting for myself and my clients. That's all I aim for and I'm happy with that.
Just don't delusion yourself into thinking you'll get rich with AdSense. Very few do and even fewer sustain their success. Usually, they end up getting banned.
HTH,
James
Insanity can be defined as "doing the same thing over and over and expecting different results."
Stupidity is not a crime. Therefore, you are free to go.
