[horde] why do I get this error in horde.log

[ANANT S ATHAVALE]

Dear List,

When I click on Administration->Sessions, though it lists the  
sessions, it also generates the following error (many like the one  
below) in horde log file.
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Aug 05 2009 15:28:10 HORDE [error] [horde] Unable to read file:  
/var/lib/php/session/sess_lcicd3k02ilrdmnj5ccuh27ru6 [pid 20986 on  
line 39 of "/home/horde/lib/Horde/SessionHandler/none.php"]
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What could be the reason for such error?

Regards,

Anant Athavale.