Error Messages during Installation Process

Hi, I receive the following error messages when trying to install Gallery 2.3

Quote:
Warning: session_start() [function.session-start]: open(/var/php_sessions/sess_05d8adc1c7d69089f70c695aec3f3622, O_RDWR) failed: No such file or directory (2) in /hermes/web10/b1423/pow.gre107/rgp-photography.ch/lib/support/GallerySetupUtilities.class on line 357

Warning: session_start() [function.session-start]: Cannot send session cookie - headers already sent by (output started at /hermes/web10/b1423/pow.gre107/rgp-photography.ch/lib/support/GallerySetupUtilities.class:357) in /hermes/web10/b1423/pow.gre107/rgp-photography.ch/lib/support/GallerySetupUtilities.class on line 357

Warning: session_start() [function.session-start]: Cannot send session cache limiter - headers already sent (output started at /hermes/web10/b1423/pow.gre107/rgp-photography.ch/lib/support/GallerySetupUtilities.class:357) in /hermes/web10/b1423/pow.gre107/rgp-photography.ch/lib/support/GallerySetupUtilities.class on line 357
Warning: Unknown(): open(/var/php_sessions/sess_05d8adc1c7d69089f70c695aec3f3622, 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 (/var/php_sessions) in Unknown on line 0

Unquote.

Can somebody help? My URL is www.rgp-photography.ch and I use a Windows Internet Explorer. Thank you.