PACE error message

I loaded this PACE thing years ago

Name of this "thing?" How can anyone tell you how to remove an item if you do not know the name of it? It's pretty hard to try to find something on a computer if you do not know the name of the item you are looking for.

See attachment screen capture.

I don't see it.

What you have is PACE Interlok, a copy-protection rootkit included with some commercial software. It's utterly hostile to your interests and serves no purpose except to keep you from exercising your fair-use rights. It gives a total stranger, the application developer, the same control over your data that you have yourself. It will destabilize your whole system and may intentionally cause a crash if it suspects you're doing something the developer wouldn't like. Not enough can be said against it.

If you recall the scandal a few years ago over the Windows DRM rootkit that Sony put on some music discs masquerading as CD's, PACE is similar to that.

What I would do in your place is contact the developer for instructions on how to remove it along with the rest of his garbage product, which of course is coded not to work unless the rootkit is installed. If he doesn't respond to your request, you'll just have to do your own research to find out where the PACE files are and remove them yourself.

~Library>Application Support>PACE Anti-Piracy
:WARNING:
Any program that involves this program will not work after removing this folder.
OnOne plugins for PS is an example of this.

This "Guitar Pro" thing evidently requires the PACE rootkit to be installed. You'll have to choose between using it and accepting the rootkit, or not using it and having control over your own computer. The choice is yours. If the "Guitar Pro" product is defective, I suggest you contact the vendor for assistance.

I have no idea. Probably because you can only install it once. The rootkit is designed to screw up your system, and it seems to be doing its job. Really, if you're going to install such things, there isn't much anyone can do to help you. The vendor took your money, let him clean up his own mess.