Fix Installous 5 error !
METHOD 1: Turn off you jailbroken iDevice then turn it on again, then restart Cydia. Now try to download any tweak from Cydia, if the “Hash Sum Mismatch” error has not been solved, jump to method 2.
METHOD 2: You have to ensure a better internet connection, in order to do this, reset you jailbroken iDevice network settings, go to Settings > General > Reset > Reset Network Settings. Also don’t forget to reboot your network hardware (modem, router and your iOS device)
METHOD 3: This method that I already used it and it worked really with me.. Which is removing Installous 4 from Cydia and remove the Hackulo.us repo, then add the repo again by going to Manage—>Sources—>Edit—>Add then add the Hackulo.us repo and after the repo is installed on your iPhone try again to download Installous 5.. Really this method worked greatly with me .. And here’s the results from my iPhone.
SOURCE : http://ijailbreaknow.com