WordPress MU

Anyone know what these warnings are and how to solve them ?
I get them right after installing the latest WPMU.

Warning: session_start() [function.session-start]: open(/tmp/sess_7055580d3bb50a41b229e1eadf93c682, O_RDWR) failed: Permission denied (13) in /home/blogg/public_html/wp-inst/wp-content/mu-plugins/wp-hashcash.php on line 29

Warning: session_start() [function.session-start]: Cannot send session cookie - headers already sent by (output started at /home/blogg/public_html/wp-inst/wp-content/mu-plugins/wp-hashcash.php:29) in /home/blogg/public_html/wp-inst/wp-content/mu-plugins/wp-hashcash.php on line 29

Warning: session_start() [function.session-start]: Cannot send session cache limiter - headers already sent (output started at /home/blogg/public_html/wp-inst/wp-content/mu-plugins/wp-hashcash.php:29) in /home/blogg/public_html/wp-inst/wp-content/mu-plugins/wp-hashcash.php on line 29

Warning: Cannot modify header information - headers already sent by (output started at /home/blogg/public_html/wp-inst/wp-content/mu-plugins/wp-hashcash.php:29) in /home/blogg/public_html/wp-inst/wp-login.php on line 9

Warning: Cannot modify header information - headers already sent by (output started at /home/blogg/public_html/wp-inst/wp-content/mu-plugins/wp-hashcash.php:29) in /home/blogg/public_html/wp-inst/wp-includes/pluggable-functions.php on line 199

Warning: Cannot modify header information - headers already sent by (output started at /home/blogg/public_html/wp-inst/wp-content/mu-plugins/wp-hashcash.php:29) in /home/blogg/public_html/wp-inst/wp-includes/pluggable-functions.php on line 200

Warning: Cannot modify header information - headers already sent by (output started at /home/blogg/public_html/wp-inst/wp-content/mu-plugins/wp-hashcash.php:29) in /home/blogg/public_html/wp-inst/wp-includes/pluggable-functions.php on line 172

Warning: Unknown: open(/tmp/sess_7055580d3bb50a41b229e1eadf93c682, O_RDWR) failed: Permission denied (13) 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

Look at the last line of that warning.. there's something wrong with your server probably:
Failed to write session data (files). Please verify that the current setting of session.save_path is correct (/tmp) in Unknown on line 0

Indead, my hosting company had some trouble.
They fixed it, and now i dont get those warnings no more.