BuddyPress.org

got my answer thanks for the hint btw.

Things I did below.hope it helps others.

Do it step wise.I have macbook.

1.In your project file like mine was htdocs/coco/ search the .htaccess file.It is will present but it will be hidden or it may not be there at all.
If it is not there, create one by using some different text editor and save the file with below contents.Remove all the blank lines and spaces from the file.
RewriteBase /
#uploaded files
RewriteRule ^(.*/)?files/$ index.php [L]
RewriteCond %{REQUEST_URI} !.*wp-content/plugins.*
RewriteRule ^(.*/)?files/(.*) wp-content/blogs.php?file=$2 [L]
# add a trailing slash to /wp-admin
RewriteCond %{REQUEST_URI} ^.*/wp-admin$
RewriteRule ^(.+)$ $1/ [R=301,L]
RewriteCond %{REQUEST_FILENAME} -f [OR]
RewriteCond %{REQUEST_FILENAME} -d
RewriteRule . – [L]
RewriteRule ^([_0-9a-zA-Z-]+/)?(wp-.*) $2 [L]
RewriteRule ^([_0-9a-zA-Z-]+/)?(.*\.php)$ $2 [L]
RewriteRule . index.php [L]
<IfModule mod_security.c>
<Files async-upload.php>
SecFilterEngine Off
SecFilterScanPOST Off
</Files>
</IfModule>
# BEGIN WordPress
<IfModule mod_rewrite.c>
RewriteEngine On
RewriteBase /coco/
RewriteRule ^index\.php$ – [L]
RewriteCond %{REQUEST_FILENAME} !-f
RewriteCond %{REQUEST_FILENAME} !-d
RewriteRule . /coco/index.php [L]
</IfModule>

# END WordPress

2.Most important step.Make the file writable.right click on fileand click get info .click the lock icon on the extreme corner of the window .then provide all the users with write and read permission.

3.Now login as wpadmin. Go to settings, permalink and just click save changes button.No need to change anything there.This will actually update your .htaccess file automatically that you created now and will update it with your project path like localhost/ to yourprojectname/ (i.e the last line in the file coco/index.php)

Now go and hit the register button(my case register button gave me 404 error and previously 500 internal server error) .It will show the register page and thats how I solve the problem.

Also, I think if we mess up with .htaccess file contents or permissions the we get 500 internal server error.

hope it helps someone!:)

We can close the thread!