Permalink problem (upgrading 2.1 to 2.5)

I think you can sort this issue by editing .htaccess

yep, some well written rewrite conditions and rules will solve this no problem.

Trailing Slash Problem

The solution to this subtle problem is to let the server add the trailing slash automatically. To do this correctly we have to use an external redirect, so the browser correctly requests subsequent images etc. If we only did a internal rewrite, this would only work for the directory page, but would go wrong when any images are included into this page with relative URLs, because the browser would request an in-lined object. For instance, a request for image.gif in /~quux/foo/index.html would become /~quux/image.gif without the external redirect!

So, to do this trick we write:

RewriteEngine  on
    RewriteBase    /~quux/
    RewriteRule    ^foo$  foo/  [R]

The crazy and lazy can even do the following in the top-level .htaccess file of their homedir. But notice that this creates some processing overhead.

RewriteEngine  on
    RewriteBase    /~quux/
    RewriteCond    %{REQUEST_FILENAME}  -d
    RewriteRule    ^(.+[^/])$           $1/  [R]

**from https://httpd.apache.org/docs/2.0/misc/rewriteguide.html

Well, first of all if I think that .htaccess will resolve the problem than he best and the easiest way to get it done is copy & paste the previous / old .htaccess file to the new one.and I did the same but still the categories are showing without /

I have used the robots-meta plugin to solve the problem of the missing trailing slash. One of the options you can turn on in that plugin’s admin is to force WP to always use the trailing slash. Works well.

Question also asked here:
https://comox.textdrive.com/pipermail/wp-pro/2008-June/000993.html

Hi
see this 5 step tutorial that tells you how to add trailing slash to a category. Please note this is only for wordpress 2.6+
https://bloggerholic.com/wordpress/how-to-add-trailing-slash-to-a-category-144.htm