Database Error with Several Modules

I get the following error not only regarding the GSitemap module, but also regarding the Flexinode module and other modules I have installed:

user error: Duplicate entry '5' for key 1
query: INSERT INTO gsitemap (nid, last_changed, priority_override) VALUES(5, 1141137086, NULL) in /home/xplode/public_html/includes/database.mysql.inc on line 66.
warning: Cannot modify header information - headers already sent by (output started at /home/xplode/public_html/includes/common.inc:384) in /home/xplode/public_html/includes/common.inc on line 192.

The element of the error that is common also for the other modules is the last part of it:
warning: Cannot modify header information - headers already sent by (output started at /home/xplode/public_html/includes/common.inc:384) in /home/xplode/public_html/includes/common.inc on line 192.

I have a 4.6.5 installation. I also have the DBA Module (Data Base Manager) installed and was able to easily upload tables for several of the modules, without needing to use PhpMyAdmin.

THE RESULT of this error is very odd. Drupal, instead of adding new nodes when a new blog is added, gives the error and at the same time overrides an existing blog's path URL with the new path URL. So I got two path URL's messed up until I unchecked the GSitemap module again. I am very frustrated because I find this module very ingenious and important.

Please help. Perhaps this error is also at the basis of other errors I receive regarding the Flexinode module. And the Weblinks module is just impossible to get running. All the errors I get are database errors.

There is one strangety. I had installed Drupal on a sub-web first and the MySQL database was
prefix_drpl1

Then I uninstalled Drupal and strangely enough the database was NOT erased.

Then I installed Drupal anew, this time in the root web. And the system created the database
prefix_drpl2

and in the error messages, when a table is missing, the system refers to:

prefix_drpl12.xyztable is missing ...

Does that mean the system uses BOTH databases at the same time??? (I ask this question because I wanted to erase the old drpl1 database)