I have installed this on 1.5.5e

The install works fine, however in Tools > Sitemap XML I get the following screenshots:
Click image for larger version.  Name: Screen Shot 2017-06-30 at 11.24.31.jpg  Views: 49  Size: 18.3 KB  ID: 17117

Click image for larger version.  Name: Screen Shot 2017-06-30 at 11.25.22.jpg  Views: 64  Size: 23.3 KB  ID: 17118

If I click the button to upgrade, it does something but then the screen remains the same asking me to upgrade the database.

Can you help please?