I'm going to add answers to any questions users had in the past.
The start button is only enabled when PVP.net Client is running. It wouldn't do anything anyway when the game is not running, so I decided to disable it to make that clear. Further more, the program is currently using PVP.net string to find the window so you might need to turn the client to english. If the PVP.net client is running but the button is still disabled please file an issue.
Typically, this happens because you're running PVP.net Client in Administrator mode. For security reasons, OS protects Administrator's windows from non-administrator programs, such as mine. If you want to run PVP.net Client as administrator, you will also have to run the AutoClient as administrator. It is recommended that you do so using this batch file. In version 3, this will be handled automatically for you.
This problem happens to you because you're running an outdated version of Java Runtime Environment (JRE). AutoClient requires Java 1.8, which can be downloaded here: http://www.oracle.com/technetwork/java/javase/downloads/jre8-downloads-2133155.html
If you let program accept games and then not play, you get to low priority queue. And if you do it still, they will ban you. But as long as you play games you've accepted, I think there is no problem.
Officially however, this tool is not allowed by Riot. From Terms of Use:
ix. Using any unauthorized third party programs, including mods, hacks, cheats, scripts, bots, trainers and automation programs that interact with the Software in any way, for any purpose, including any unauthorized third party programs that intercept, emulate, or redirect any communication between the Software and Riot Games and any unauthorized third party programs that collect information about the Game by reading areas of memory used by the Software to store information;
But since it generates fake click events only on PVP.net client and doesn't interact with the game itself, it's not network hack and I don't think they would ever care to do anything about it.
If you get this error:
java.class.lang.NoClassDefFoundError: Could not initialize class cz.autoclient.autoclick.windows.ms_windows.MSWindow
Try to uninstall java and install the latest version of the Java from java official website.