What were you applying the class to what widget and where is this published? I will try to replicate this locally and see if I goofed on coding.
For that error, you may want to check this out which I think is related to server space: http://wordpress.org/support/topic/incompatible-archive-pclzip_err_bad_format-10
As for uploading a plugin, you can do this also by unzipping the download and then manually uploading (through FTP program) the plugin folder into this location:
/wp-content/plugins/
But for the plugin, you should be able to install the plugin like a regular WP plugin… going to Plugins >> Add New >> Upload
