My problem is that every time I do some operation with an URL like the following one: https://nttt.dttt.com:8443/svn/nttt/Med/trunk I get
Server sent unexpected return value (403 Forbidden) in response to OPTIONS".
The user and password I supplied was correct, so no problem there.
I don't know where the problem lies, I don't know if it is the server(on witch I don't have any control) or my Tortoise client.
I don't think it is TroitoiseSVN. The problem most likely is that you don't have access to full tree or all HTTP operations. Try accessing these URLs in your browser:
https://nttt.dttt.com:8443/svn/nttt
https://nttt.dttt.com:8443/svn/nttt/Med
https://nttt.dttt.com:8443/svn/nttt/Med/trunk
And see if you get any 403 errors. Otherwise you will need to talk to your system administrator to fix the rights.