Just an update:

I'm using the option:
"Subdomain of basedomainhttp://url_name.mydomain.com/"
On the URL Options of blog settings....

If i mark the option to use extra path, the posts will work because b2evo inserts index.php/blogname/2009/01.......

but the idea is to use a subdomain not an extra path. (this was working before the update. )

EDIT: Another update:
if i try to access the post:
http://blog.mydomain.com/2009/01/28/my_post
inserting manually the index.php in the middle, he will redirect to the wrong address again...
http://blog.mydomain.com/index.php/2009/01/28/my_post redirects to http://blog.mydomain.com/2009/01/28/my_post and then i receive a 404 error.

ps: i'm not using mod_rewrite or any custom redirect...
ps2: i wasnt using any big modifications or plugins on this blog before the upgrade, just captcha images that i already disabled

thanks again

Have you tried the another option, a full path and write your full addres in the input?

You mean the absolute path option?
Yes i tried, same problem....

I even tried to insert index.php at the end of the absolute path but things just got worst.
:(

If http://blog.mydomain.com/index.php/2009/01/28/my_post is redirecting to http://blog.mydomain.com/2009/01/28/my_post is due to our canonical urls...

Have you tried setting a absolute path, adding the index.php in the end?

Walter wrote:

If http://blog.mydomain.com/index.php/2009/01/28/my_post is redirecting to http://blog.mydomain.com/2009/01/28/my_post is due to our canonical urls...

Have you tried setting a absolute path, adding the index.php in the end?

Yes, i tried... but then when i access http://blog.mydomain.com/index.php looks like the index.php do not recognize the url and i land on the wrong blog (default one).

i have 2 blogs on same b2evo.
1st http://me.mydomain.com (default)
2nd http://blog.mydomain.com

I Found it!!

I Forgot about the .htaccess file for the rewrite rules.

During the upgrade i removed all the files and just uploaded the media folder.

RewriteEngine On

# Redirect anything that's not an existing directory or file to index.php
RewriteCond %{REQUEST_FILENAME} !-d
RewriteCond %{REQUEST_FILENAME} !-f
RewriteRule ^  index.php

Thanks for the help Walter :)