Problem with installing Poll component

Hello,

I use joomla 2.5.1 and i bought the new version of the community polls component (com_communitypolls_v3.1.2). But I am unable to install this component. The documentation advises that the API component which is com_cjlib_v1.5.5 be installed first. I did so and also installed the modules and plugins only can't install the component.

Error messages:
HTTP Error 500 (Internal Server Error): An unexpected condition was encountered while the server was attempting to fulfill the request.

How can I fix this?
Bob