I really need to change my blog url (as someone's found it), but
everytime i try to change it to something else, i'll get an error page.
 Then when i start over and try again, it will say that the url is
unavailable.

Some of the new urls i've tried, i can understand that they might
really already be taken, but there are others that i find it very
difficult to believe are taken.  I mean, i've tried just random letter
and number things, and the same thing keeps happening.  Nothing i try
works, no matter how random.

Again, i go and type in a new url, get an error message, start over
again and type in a url, then get a message that the url is not
available.

Why could this be happening?