Can someone please advise on PHP warnings in the error log

Hi I'm getting this showing up in the error logs on a regular basis


2012-02-15 21:14:17 - PHP Warning: unlink(/web2/user37385/website/system/cache/cache.currency.1329337785) [<a href='function.unlink'>function.unlink</a>]: No such file or directory in /web2/user37385/website/system/library/cache.php on line 14
2012-02-15 21:14:17 - PHP Warning: session_start() [<a href='function.session-start'>function.session-start</a>]: Cannot send session cookie - headers already sent by (output started at /web2/user37385/website/index.php:104) in /web2/user37385/website/system/library/session.php on line 11
2012-02-15 21:14:17 - PHP Warning: session_start() [<a href='function.session-start'>function.session-start</a>]: Cannot send session cache limiter - headers already sent (output started at /web2/user37385/website/index.php:104) in /web2/user37385/website/system/library/session.php on line 11
2012-02-15 21:14:17 - PHP Warning: Cannot modify header information - headers already sent by (output started at /web2/user37385/website/index.php:104) in /web2/user37385/website/index.php on line 179
2012-02-15 21:14:17 - PHP Warning: Cannot modify header information - headers already sent by (output started at /web2/user37385/website/index.php:104) in /web2/user37385/website/system/library/currency.php on line 45

Using v1.5.1.3

Thanks

Emma