Install plug in for Joomla

Congratulation for piwik, it is very interesting web analytic, but I have a problem to install plug in 213: it is written:
File integrity check failed and reported some errors. This is most likely due to a partial or failed upload of some of the Piwik files. You should reupload all the Piwik files and refresh this page until it shows no error.
File size mismatch: /home/mhd-01/ (expected length: 1024, found: 1179)
File size mismatch: /home/mhd-01/ (expected length: 1688, found: 2911)
May you help me?