Here is my fix
This refers to Version 3.5.1 of Register-Plus
As I would look through my access logs I would see that there were a great deal of calls to:
all getting a 404 Error
I couldn't figure out what was calling that script until I looked through the source code of every plugin I had running (20-30 plugins.. wasn't fun)
Anyway I found the problem in:
SEARCH for this code:
and REPLACE ALL OCCURRENCES with this code: (5 of them)
<?php echo trailingslashit(get_option('siteurl'));?>
then SAVE the file and you are done.
The problem is obviously that the value of "trailingslashit(get_option('siteurl'))" is not getting echoed or printed so the url is always appended to the end of the current url. This causes a problem when the url is "http://siteurl.com/post/whatever/" but not when it is just "http://siteurl.com/"
If you are the plugin author please fix this error in the next version of Register-Plus.
Thank you and have a nice day everyone.