I frequently get an error message in my admin side of my Joomla based web site stating that the connection to the database has been lost. sometimes I have to refresh the page a couple of times for the admin page to come up without this error.
Does the MySQL used associated with the Joomla installation have all permissions assigned to it? If not, this can cause some problems with certain functions. Also, what is your site, and I'll see if it's happening from my computer.