This may be a problem with your host. In any event the web server should give more information in an error log.

Can someone do an FAQ about this... it seems like a common problem.
http://forums.b2evolution.net/viewtopic.php?t=5223

I'm having the same error... Running XAMPP 1.0 on windows..
Apache - 2.0.53 (Win32)
PHP - 5.0.4
MySQL - 4.1.11

When i click on the categories tab - (as the default admin - so I have got access to it) - it will sit there and do nothing....

The following is my Apache Log:

[Tue Nov 08 14:26:41 2005] [notice] Apache/2.0.53 (Win32) mod_ssl/2.0.53 OpenSSL/0.9.7f PHP/5.0.4 configured -- resuming normal operations
[Tue Nov 08 14:26:41 2005] [notice] Server built: Apr 8 2005 10:55:39
[Tue Nov 08 14:26:41 2005] [notice] Parent: Created child process 6492
[Tue Nov 08 14:26:43 2005] [notice] Child 6492: Child process is running
[Tue Nov 08 14:26:43 2005] [notice] Child 6492: Acquired the start mutex.
[Tue Nov 08 14:26:43 2005] [notice] Child 6492: Starting 250 worker threads.
[Tue Nov 08 14:26:57 2005] [error] [client 127.0.0.1] File does not exist: C:/apachefriends/xampp/htdocs/favicon.ico
[Tue Nov 08 14:27:01 2005] [error] [client 127.0.0.1] File does not exist: C:/apachefriends/xampp/htdocs/favicon.ico
[Tue Nov 08 14:27:01 2005] [error] [client 127.0.0.1] File does not exist: C:/apachefriends/xampp/htdocs/b2evo/b2evolution/blogs/htsrv/styleswitcher.js, referer: http://localhost/b2evo/b2evolution/blogs/admin/b2users.php
[Tue Nov 08 14:27:01 2005] [error] [client 127.0.0.1] File does not exist: C:/apachefriends/xampp/htdocs/favicon.ico
[Tue Nov 08 14:27:30 2005] [error] [client 127.0.0.1] File does not exist: C:/apachefriends/xampp/htdocs/favicon.ico
[Tue Nov 08 14:27:36 2005] [notice] Parent: child process exited with status 3221225477 -- Restarting.
[Tue Nov 08 14:27:36 2005] [crit] (22)Invalid argument: unable to replace stderr with error_log
[Tue Nov 08 14:27:36 2005] [crit] (2)No such file or directory: unable to replace stderr with /dev/null
[Tue Nov 08 14:27:37 2005] [notice] Apache/2.0.53 (Win32) mod_ssl/2.0.53 OpenSSL/0.9.7f PHP/5.0.4 configured -- resuming normal operations
[Tue Nov 08 14:27:37 2005] [notice] Server built: Apr 8 2005 10:55:39
[Tue Nov 08 14:27:37 2005] [notice] Parent: Created child process 5824
[Tue Nov 08 14:27:38 2005] [notice] Child 5824: Child process is running
[Tue Nov 08 14:27:38 2005] [notice] Child 5824: Acquired the start mutex.
[Tue Nov 08 14:27:38 2005] [notice] Child 5824: Starting 250 worker threads.
[Tue Nov 08 14:27:39 2005] [error] Parent: child process exited with status 3 -- Aborting.
[Tue Nov 08 14:27:39 2005] [crit] (22)Invalid argument: unable to replace stderr with error_log
[Tue Nov 08 14:27:39 2005] [crit] (2)No such file or directory: unable to replace stderr with /dev/null
[Tue Nov 08 14:27:39 2005] [notice] Apache/2.0.53 (Win32) mod_ssl/2.0.53 OpenSSL/0.9.7f PHP/5.0.4 configured -- resuming normal operations
[Tue Nov 08 14:27:39 2005] [notice] Server built: Apr 8 2005 10:55:39
[Tue Nov 08 14:27:39 2005] [notice] Parent: Created child process 7944
[Tue Nov 08 14:27:40 2005] [notice] Child 7944: Child process is running
[Tue Nov 08 14:27:40 2005] [notice] Child 7944: Acquired the start mutex.
[Tue Nov 08 14:27:40 2005] [notice] Child 7944: Starting 250 worker threads.

This is probably a bug with PHP 5.0.4.

Please upgrade to 5.0.5 - which the demo site also runs on.

There were problems with PHP 5.0.4, too.

Thanks I will check with my host