[Plugin: Joomla 1.5 Importer] Old website gives error: MySQL database not accessible

I have one site hosted with joomla and want to use wordpress for that one instead. I installed wordpress on a subdomain, and used your tool for importing one category to the one in wordpress.
That part worked fine, however, it caused the MySQL database not accessible in the main domain any longer. Fortunately I had everything backed up and was able to restore the databases.

Is there are a way to avoid this from happening while I continue to modify the subdomain to my wishes (leaving the original website untouched and on-line)?