[TYPO3] Problem linking between websites on the same Typo3 instance

[Ricardo Pereira]

    Dear list,

    I've been having problems creating links between sites hosted by the 
same Typo3 instance and I thought I would ask for help here on the list.

    My Typo3 instance hosts 2 websites with their own domain names 
(www.tdwg.gbif.org and tdwg2006.tdwg.org). On the 2nd website there is a 
page (http://tdwg2006.tdwg.org/programme/abstracts/) that contains a 
link to the first site (http://www.tdwg.gbif.org/membership/registration/).

    The problem is that the link to the first site gets modified to 
http://tdwg2006.tdwg.org/membership/registration/ and it doesn't take 
visitors to where it should take them.

    For now, I've fixed the link by replacing the domain name by the IP 
address on the link (http://192.38.28.103/membership/registration/). 
Ugly I know, but I'm desperate ;)

    Can anyone help me figure out what is wrong and how to fix it?

    I use Typo3 v3.8.1 and MTB technique for my templates. Both sites 
have domain records.

    Any help is greatly appreciated.

    Cheers,

Ricardo Pereira