[xwiki-users] XWiki space partially deleted

I wanted a metawiki space, so as the "Admin" user, I created the "XWiki" space. Realizing that we already had a "Wiki" space, I deleted the "XWiki" space. The deletion to surprisinly long time, so I got suspicious and hit "Cancel". I didn't think much of it until a few days later, when I was no longer able to log in as "Admin". That was when I remembered that the "XWiki" space is special. I had deleted a lot more than just a newly created empty space. Now I am no longer allowed to log in as "Admin" or "superadmin". Both accounts worked before, but now both give me the error message "Invalid credentials". Apparently, all users can log in with their ordinary user account, but with no admin account I can no longer re-import the XWiki pages from the XAR file. The "superadmin" account was enabled when I upgraded to the current XWiki 5.2. It was tested and working, but not any longer. How on earth to I get around this? As as side note, I am very surprised that 1) I was able to create the "XWiki" space, just as any other space, and 2) that I was able to delete the "XWiki" space with no notification about this space being vital to XWiki. Any help or pointers are highly appreciated. Kind regards, Peter John Acklam