At first I saw this message a few times and the resolution wasn't too difficult at all, after a short while of Googling etc it became apparent that an Auto Update had messed up the SQL reporting services ActiveX client and so needed another update applying.
Solution: Install the fixes below on the necessary servers and then reboot each server.
Microsoft Report Viewer Redistributable 2005 Service Pack 1 http://www.microsoft.com/downloads/details.aspx?FamilyID=82833f27-081d-4b72-83ef-2836360a904d&DisplayLang=en
SQL Server (If Different):
Security Update for SQL Server 2005 Service Pack 2 (KB954606) http://www.microsoft.com/downloads/details.aspx?FamilyID=4603c722-2468-4adb-b945-2ed0458b8f47&DisplayLang=en#filelist
To finish, open the reports window and click print, you still get the error but this time you get an ActiveX control to install, install that and rerun the report. You can now print fine.
HOWEVER - Please Note
Be warned, this only happened to me once but it might be that on Server 2008 once you have applied the update the Reporting Server doesnt even let you run reports never mind print them. I got a 404 permission denied when navigating to http://servername/reportserver and also got an error in Event Viewer
"Web service request ListExtensions to Report Server failed"
The resolution I found to this was to go into IIS 7, navigate down to ReportServer in Sites and click on Handler Mappings, then click any of the sub items and on the left click "Edit Feature Permissions" Check the Script box as well as Read box.(Not Execute). You find at that point it should run fine.
Good luck anyone else in this scenario, love to know if this works for you!