I had same problem on CentOS. Browsing log files I found the solution.

Go on:

1) From CLI:
My web installation folder is: '/var/www/html/freepbx-v3', changhe it as your environment.

go to web installation folder and run preinstall.sh or do that:

chown -R apache:apache *
chgrp apache /etc/odbc.ini
chmod g+w /etc/odbc.ini

2) From Web GUI:
Go to System - ODBC, check configuration by editing DSN Entry (should be ok)
After that select 'odbc.ini' from action (on the right) for you DSN Entry

For example you can see:
-----------
[ODBC Data Sources]
odbcname = MyODBC 3.51 Driver DSN

[FreePBX]
Driver = /usr/lib/odbc/libmyodbc.so
Description = FreePBX ODBC Connection
SERVER = 127.0.0.1
PORT = 0
USER = freepbx
Password = freepbx
Database = freepbx
OPTION = 3
SOCKET =
------------

3) CLI again:
Edit your /etc/odbc.ini and put the output from you see before.

Now you have to find/install libmyodbc version 3.xy

On CentOS you have to use remi repository and so you have to do:

- Install remi repo:
wget http://rpms.famillecollet.com/enterprise/remi-release-5.rpm
rpm -i remi-release-5.rpm

- Install needed lib:
yum -y --enablerepo=remi install unixODBC unixODBC-devel mysql-connector-odbc

After that, freeswitch expect your lib in /usr/lib/odbc and it's named libmyodbc.so

CentOS install that lib in /usr/lib named libmyodbc3.so

Simply create a soft link:

mkdir -p /usr/lib/odbc
cd /usr/lib/odbc
ln -s ../libmyodbc3.so libmyodbc.so
ln -s ../libmyodbc3_r.so libmyodbc_r.so
mkdir -p /usr/lib/odbc
cd /usr/lib/odbc
ln -s ../libmyodbc3.so libmyodbc.so
ln -s ../libmyodbc3_r.so libmyodbc_r.so

4) GUI again:
Browse to Connectivity - SIP Interface and select action 'Edit SIP Interface'

Go to bottom and check 'Use ODBC', save and .... well done! It's working

Med