Hello,
In order to help you, I need more information from you. You seem to run the version for Joomla! 1.5. What are your module parameters? What are your contacts, categories... Do you have a URL I can look at?
Finally, using the forum does not prevent you from being polite. Thank you for your understanding.

Hello,
I still need more info.
What are your module parameters? What are the contacts, categories you are using with Trombinoscope? You are getting an error on the parameter that contains the contact list. What is the version of PHP you are using?

Ok, got where the problem is: you entered the category name in the 'categories' field, but in the Joomla! 1.5 version you need to enter the category id or ids (comma separated).