Unable to login with Piwik 1.1.1

I have cleared my browser chache. I even have reinstalled piwik.
Nothing works for me.

PHP Version 5.2.6
FreeBSD 7.0

there is a bug report: Broken json extension: Login not working in 1.1.1 for some users · Issue #1958 · matomo-org/matomo · GitHub
please post your details there