Can you see that post in backoffice?

No, I can't see it in the backoffice only in the MySQL database through PHPMyAdmin.

Check the "post_main_cat_ID" value for that post, is it a real ID of the category you created it in?

It is the real ID.

Set post_datestart value to some date in the past, e.g. a month ago. You should then see the post in backoffice.

You can also try this:
Find main category category ID in "evo_categories" and make sure the cat belongs to the right blog "cat_blog_ID".

Then open this URL in backofice
/admin.php?blog=22&ctrl=items&cat=55

There's also a way to reset filters in backoffice
/admin.php?ctrl=items&filter=reset&blog=33

Sam2kb, I did all as specified but still the post is not shown anywhere but in the Database.

gcasanova wrote:

My b2evolution Version: 4.1.x

I'm finding it impossible to post into the main blog using some categories from the main blog.
The post appears in the MySQL database as published but it's not shown in the actual live blog.
Any help?

is there a pattern which categories these are ? a link to the blog might help.

I haven't found any pattern. I thought I did, that the pattern was the categories from Main Blog that had a description and that the description had accented characters. But then I found a category with that pattern and which posts were published without problems

The blog is http://www.literanova.net

The post that is not appearing published but that is present in the database has the following link: http://www.literanova.net/index.php/l-enfant-terrible-1

It was published under main Categories listed in the main blog's Categories.

The same post was published fine under a different Category from "blog8". It automatically changed its URL to

http://www.literanova.net/index.php/l-enfant-terrible-2 

So if that post is published fine in another category, what happens if you now change its category to the category you really want?

What happens if you change the category back after that?

Can you compare, field by field the 2 entries (the one that works and the one that doesn't) in MySQL?

Are you using any third party plugins?

Before trying the first hints, these are the Plugins I have installed:

AdSense - Installed but OFF
Agregado para pings genérico - Installed but OFF
AM Assign Author - Installed but OFF
AM Audio Player - Installed but OFF
Archives Widget
Auto Links
Auto P
Basic Antispam
BB code
Blogalaxia Tags - Installed but OFF
Bookmarklet
Embed Flash
Enlaces Wikipedia
Extensión de pings a Ping-O-Matic
Hot Topics
Imágenes captcha - Installed but OFF
More Quick Tags
Nivo Slider Widget
Ping b2evolution.net
Quick Tags
Quick Text
Quick Upload
Real Tag Cloud
Save and review / Autosave
Smilies - Installed but OFF
Social Buttons
Sorted Public bloglist
Star Rating
STW Webshots
Subscriptions
Texturize
Thumbnail
TinyMCE
Tweetmeme - Installed but OFF
Twitter plugin
Video Plug
Website Thumbshots
YouTube plugin

So if that post is published fine in another category, what happens if you now change its category to the category you really want?

It remains published and visible.

What happens if you change the category back after that?

It's still published and visible.

Can you compare, field by field the 2 entries (the one that works and the one that doesn't) in MySQL?

Except for Post_Id, post_datestart, post_datecreated, post_modified, post_urltitle, post_canonical_slug_ID, post_tiny_slug_ID. post_main_cat_ID. post_views, all the rest are the same.

So if you change the category and it stays visible, all I can think of is that:

-either one of your many plugins is doing something weird

or

- you actually have no problem except for a 10 minute cache delay:

http://b2evolution.net/man/user-guide/faq/blog-is-not-updated

I think the problem must be one of the plugins because when publishing under some categories the post never shows.

I will try and uninstall as many plugins as possible...