It sounds like there's a file missing, but since you've tried two different versions, something is strange.
Still, the 404 error indicates that the wrong page URL is being typed into the address bar when trying to access the BB admin...If a module such as xml parser were missing, it would give a 500 server error, not a page not found error.
Your admin URL should look something like:
Make sure the folder path is correct.
If double-checking this URL doesn't work (don't reinstall), email your FTP info to me and either Kirill or I will take a look.