Postfix can't access MySQL after upgrade Ubuntu/MySQL

A few years ago I have hired someone through this site to set up my mail server. Last saturday I upgraded Ubuntu to 12.04, and in the process MySQL was updated to 5.5 I retained all configuration files, but Postfix can't access anymore. I presume the problem is in the connection to MySQL but I can't find the problem. As I can't disclose passwords I propose we work trough skype, and I share my desktop so I can enter passwords when necessary. Please post a fixed amount for this assignment (and not an hourly fee), you can't make me happier than to solve this in 5 minutes! However, I think a maximum of 2 hours should suffice for an expert, so if after 2 hours the problem ain't solved (and we aren't on the road to solve) the assignment will be given to another coder.