After installation of zenphoto 1.2.1 in my wp 2.6.3 I got that error messages on my screen:

`

Warning: session_start() [function.session-start]: open(/tmp/sess_b8e1405a91bed491ecef97a29160497f, O_RDWR) failed: No such file or directory (2) in /zenphoto/zp-core/admin-functions.php on line 9

Warning: session_start() [function.session-start]: Cannot send session cookie - headers already sent by (output started at /zenphoto/zp-core/admin-functions.php:9) in /zenphoto/zp-core/admin-functions.php on line 9

Warning: session_start() [function.session-start]: Cannot send session cache limiter - headers already sent (output started at /zenphoto/zp-core/admin-functions.php:9) in /zenphoto/zp-core/admin-functions.php on line 9

Warning: Cannot modify header information - headers already sent by (output started at /zenphoto/zp-core/admin-functions.php:9) in /zenphoto/zp-core/functions.php on line 2025

Warning: Cannot modify header information - headers already sent by (output started at /zenphoto/zp-core/admin-functions.php:9) in /zenphoto/zp-core/auth_zp.php on line 44

Warning: Cannot modify header information - headers already sent by (output started at /zenphoto/zp-core/admin-functions.php:9) in /zenphoto/zp-core/admin-functions.php on line 200

`

Then I can see administration panel.
And under administration panel I have next error messages:

`

Warning: Unknown: open(/tmp/sess_b8e1405a91bed491ecef97a29160497f, O_RDWR) failed: No such file or directory (2) in Unknown on line 0

Warning: Unknown: Failed to write session data (files). Please verify that the current setting of session.save_path is correct (/tmp) in Unknown on line 0

`

Headers already sent errors may mean you have an extra space at the beginning of a php file. Check any files you may have opened, see if there is a space or hard return before the code starts.

The session error is something in php.ini, I found your post looking to solve the same problem.