Blogger's invitation process is terrible.  I have tried using it with limited success.  It especially does not work well if you have a Hotmail a/c.  The official help page admits this.  I am currently trying to persuade Blogger that their invitation process is BROKEN.  They are still in denial, I think.  I thought all Google's technology was supposed to work reliably.  Well, this does not.  It is really a shame.