Yes this is because Solution named iscontentquerywebparts.cab already exists on your SharePoint Server.
Pleae go to Central Administration -> Operations -> Solution Management.
Here in the list of Solutions you will find iscontentquerywebparts.cab
Click on it, then Retract Solution and then Delete it.
Now when you install PKSFull.xml you wont get the error. If you are doing a clean install make sure there are no solutions deployed earlier.