Error Log TOO BIG… Why?

Hello everybody.
My problem is that my Error.log file continues to become too big (300-400 MB), filled of a lot of problems like this:

[23-Sep-2008 20:52:43] PHP Warning: cannot yet handle MBCS in html_entity_decode()! in /home/********/public_html/sito/wp-content/plugins/wp-postviews/wp-postviews.php on line 260

Before I obtain this error, there was one similar but with the plugin “Postratings” which I deleted to resolve the problem. But it didn’t work…

Can you please tell me what’s the source of this error? Neither the upgrade from WP 2.5 to 2.6 solved it…

Thank you.

Edoluz