Hi Goldies, I have had same problem with this module (Pretty Clean URLS), it simply did not work and Milozs (MyPresta) stopped responding for many days so in the end I deleted the module and installed this one: SEO Pro All-In-One. URL cleaner, which worked straight out the box.
I've asked MyPresta for a refund but have had no response yet.
It's a shame because all previous modules from MyPresta worked well and Milosz was very fast at responding until we downloaded the Pretty Clean URLS module - I will need many more moudles before my project is complete so it's not a good business move for him - if he'd said sorry not working and provided a refund, then would be easy to move on and consider his modules in future...but now it's not like that.