[pmwiki-users] session_write_close() error in captcha recipe

[SteP]

Sorry for the long message. In summary, I need a working captcha solution, can someone help me?

Below is what I've done so far. A strange php session_write_close() error message shows up, and I don't 
know how to fix it.

I started off wanting to use recipe Cookbook.Captcha. First I tried it with Abyss server - the captcha 
image was null/zero/empty, and there were no error messages to help troubleshooting.

Then I tried it with a LAMP apache2 server (Uniform Server) - still got no image, but this time I got the 
following errors:

Warning: session_write_close() [function.session-write-close]: open(/tmp\sess_
41jec335ib4f70ap4tqmf58h95, O_RDWR) failed: No such file or directory (2) in V:\www\virtualhost\pmwiki
\cookbook\captcha.php on line 79

Warning: session_write_close() [function.session-write-close]: Failed to write session data (files). Please 
verify that the current setting of session.save_path is correct (/tmp) in V:\www\virtualhost\pmwiki
\cookbook\captcha.php on line 79

Warning: Cannot modify header information - headers already sent by (output started at V:\www
\virtualHost\\pmwiki\cookbook\captcha.php:79) in V:\www\moreatless\p\pmwiki.php on line 1079

What's odd is that I could see non-empty session data file /tmp\sess_41jec335ib4f70ap4tqmf58h95 in V:
\bin\uniserver\udrive\tmp. Apparently session_write_close() couldn't find it, hence the error messages. 
Could it be an apache configuration issue? Perhaps session_write_close() expects /tmp under 
virtualHost's root (V:\www\virtualhost) and can't see the real /tmp in apache2 server's directory (V:\bin
\uniserver\udrive).

httpd.conf includes:

# VIRTUALHOST.LOCALHOST
<VirtualHost *>
ServerName virtualhost.localhost
DocumentRoot v:/www/virtualhost
</VirtualHost>

There are other similar virtual hosts defined in httpd.conf.
Note that  the captcha recipe still fails (with no error message) with Abyss server, which isn't a apache 
server).

In summary, I would be happy to use any (robust) captcha solution working. Please advise me, thanks in 
advance.

--SteP