After transfer of test site to live site all pages---but the frontpage---return (Apache) "Not Found" errors.

Hello,

First of all I would like to apologize for possibly posting this problem in the wrong support forum and perhaps asking a trivial question. All the same, I did spend many hours browsing the dupal pages in search of a solution to my problem, but although some problem/solution topics seemed quite similar, none did offer a working solution. Any reference to the solution is thus equally appreciated!

Okay, here goes:
I have recently been appointed the task to develop a website for my employer---a small teachers office---that has to replace an outdated hmtl-page. The website is supposed to give information about the group and have pages listing all courses or projects run by our staff.
Since I will be expanding the site with some functionalities over the next months, I thought it would be appropriate to develop in a test site and then transfer everything to a live site as soon as everything was working.

The site is hosted on a server that I do not maintain myself, and it is in a sub-directory of the main office url: www.example.com/oursite/
Previously, the test site was running fine under www.example.com/oursite/testversion/

So, after renaming the old html-page to a backup name, I copied all the directories inside the "testversion" dir to the directory that housed the former html-page.
Then, I used PHPMyAdmin to export the whole "testversion"database to a .sql file. Afterwards, I imported the file in the "liveversion" database.
Previously, I would have to chmod -R o+rX * the directory containing drupal to get everything to work on the "testversion" site. So, now I did the same for the "liveversion" site.
I also changed the $base_url line in /sites/default/settings.php: I removed the "/testversion" at the end.

So by now, I would expect the site to show up in the browser. At first glance it did show up--front page was there---however, any link I clicked would not open and instead show:

"Not Found

The requested URL /oursite/node/2 was not found on this server.
Apache..etc."

When typing www.example.com/oursite/?q=user I would get the normal login screen. Logging in worked, but still only the front page was visible (although when trying to log out I would get the same Not Found error)

(NOTE: the first time I edited /sites/default/settings.php: I mistakenly left a trailing slash.. when I tried to access the liveversion website then, I was able to see the frontpage but the error pages for other parts of the site showed a double slash (//) so I went back to settings.php and removed the trailing slash)

--

I am not sure what is causing this error. I though that maybe my improper $base_url edit (with trailing slash) messed things up in the database, so I emptied the database and re-imported the "testversion" database.

Please advise or direct to a previous solution.

Any help appreciated! ;-)