While upgrading wordpress from 2.8.1 to 2.8.2 or 2.8.2 to 2.8.3 (or any other versions) i got this error saying:
With the release of wordpress 2.8 there is an error while installing some plugins or anything on the wordpress from admin panel. This error was not fixed till wp 2.8.1
The error can be solved by downloading this new http.php file from official WordPress site and over writing it on your current file.
Hope it solves the issue.
Please note, if you have recently upgraded your wordpress and are getting this issue (if you have solved it last time) make sure that you have replaced the http.php file in your wordpress with the above file again.
If you are still facing the pclzip_err_bad_format (invalid archieve structure) error when you upgrade the wordpress, please make the backup of your current wordpress install and do the manual upgrade. You can see the article on manual upgrade in the related articles.
This will solve the issue with upgrade from 2.8.1 wordpress version to 2.8.2 or from 2.8.2 to wordpress version 2.8.3