DB Error: extension not found

I had this error and for about two weeks could not find the problem. I uninstalled lamp, reinstalled it several times and still had the same problem. I am using Ubuntu 9.10 as my O.S. Instructions follow same

From my research I found out that the mysql.so extension was not written to the php.ini file, so this is what I did to correct the error:

1.  gksudo gedit /etc/php5/apache2/php.ini
2.  ctrl+f and enter "extension"
3.  look to see if ";extension=mysql.so" is in the file
4.  if it is, remove the semi-colon. the semi-colon represents a comment so it is actually commenting out the extension that is needed

in my case though, the extension was not written to the file at all, so if this is the case do this
5.  copy and paste "extension=mysql.so" within the section for "Dynamic Extensions"
6.  restart the apache server: sudo /etc/init.d/apache2 restart

that should do the trick.