C# Set Registry Value throws UnauthorizedAccessException

Follow the following code, note the additional true argument:

RegistryKey key = Registry.LocalMachine.OpenSubKey("SYSTEM\\CurrentControlSet\\services\\Tomcat7",true);
key.SetValue("Start", 2, RegistryValueKind.DWord);

This might help ,

Link to similar issue on stack overflow

looks like you are opening the key read only … Google is your friend.