I'm assuming this is Windows, but that doesn't really matter. Try putting the whole path to svnsync in the system call... eg: "c:\program files\svn\svnsync" or whatever it may be.

After that, try the pre-commit again.

This is a common issue on Unix when running a script from the scheduler... runs fine on the CLI, but the environment isn't set up the same when running it from cron.

-stevieb