Hello,

when I search my forum on Google it will say that the description is not available due to my robots.txt file. Also, if I search the contents of a specific post, it doesn't show up on Google but it does on Bing.
It is allowed for guests to see.

I didn't even install such a file nor do I know how to do it. Please help me to get rid of it. What are the possible causes? 

I'm using a meta tag called "google-site-verification" and "google-translate-customization".

The Google bot only doesn't have access to some specific pages, like:

Code:

Disallow: /abuse
Disallow: /admgt/
Disallow: /contact
Disallow: /donate
Disallow: /go/
Disallow: /login
Disallow: /modcp
Disallow: /post
Disallow: /privmsg
Disallow: /spa/
Disallow: /sta/

The rest of the website should be indexed...

What you are telling should be becouse your sub-forums are protected by login. So only registed users could login. The google bot can access that pages and doesn't show the description of the topic/page..

The sub-forums which don't show up on Google are accessible for guests. Bing does pick them up and I can view the content as guest. So you're saying that there's nothing wrong with the robots.txt file? But why does it say that site description etc. are not available? It worked a while ago, I just don't know what changed and why some sub-forums/ topics are no longer picked up by Google.

Can you give a example?