I've managed to fix the problem...now its okay. The problem was i think with the threading. In my app i have four forms; My Software, Print Loader, Printer App, And Report Viewer. Long story short, in order to print from my software the Print Loader has to find and run the appropriate "Printer App" requested by My Software. Back then i had this really cool idea of displaying the Print Loader with the message "Please wait while Printer is being loaded..." which can be moved while the "Printer App" is being loaded. The "Printer App" is run on a separate thread and when it appears the "Print Loader" exits. This is where i get the problem with VISTA (but its fine with Win XP). When i view the report from the ReportViewer my report shows but it hangs when i press the print or export buttons (i have to close the whole software). The solution was to remove this cool idea and just load the Printer App without threading.

Or may be i'm doing something wrong? Anyway its fine now.