BUG when start to setup the site in Modx with mysql

I can install all pack with no problem. I enter with my login and when I try to start to setup, the first error appears. An example is if I try to change the site name in the first screen and click in save. After this, I lost all setup from the site, all text linked in template are lost. So, are there a tip to pass this error? Are there a way to avoid it?

Warning: mysql_num_rows(): supplied argument is not a valid MySQL result resource in /home/httpd/vhosts/renalvet.com.br/httpdocs/v2/manager/actions/welcome.static.php on line 85

Warning: mysql_num_rows(): supplied argument is not a valid MySQL result resource in /home/httpd/vhosts/renalvet.com.br/httpdocs/v2/manager/actions/welcome.static.php on line 154

I´m trying to use other CMS because, this error always happen if I change information in setup....

Thanks if someone could help me!

Sounds like either some files failed to upload correctly or you are losing connection to your database periodically.