Apple has released a new version of iTunes, iTunes 9.1 which changes how certain things work. If you have upgraded to iTunes 9.1, several programs will start giving you an error that ASL.dll is missing.
The solution for this is simple, you will need to place the Blackra1n executables in the Apple folder under Common files in Program Files. The folder would be located in the following locations:
32 Bit – C:\Program Files\Common Files\Apple\Apple Application Support
64 Bit – C:\Program Files (x86)\Common Files\Apple\Apple Application Support
Once you copy the blackra1n executable to the above folder, create a shortcut for it on the desktop and double-click it to run it as usual.
Update: If you continue having problems with Blackra1n, you can use the new Spirit tool to jailbreak iPhone OS 3.1.3 and others.