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Hooray, I've learned how to make custom tools and how to organize them to my working style, but yesterday I made some that weren't there this morning. How could I have lost them? I've done this the same way in the past and had no problems saving the changes. What could I have done wrong?

Did you save them on a HD or just in your Project?

Yes, I discovered when opening the file this morning that in fact, by mistake, I'd only saved the project on the external HD. For future ref, does this mean that TVP won't save the "add actions" if you save the project just on the external HD?

Have you looked into your "Windows" tab on the main menu? If you select Custom Panels in the drop down menu, you should see a list of all custom panels you have named and saved. Some might not be checked, which will happen if you intentionally or accidentally click on the corner "X". All you need to do is to select the unchecked one to bring it back to your GUI -- but this is not really a safe way to keep your CPs. If you lose or delete your project you may lose the CPs you had created in it. This is why it is always safe to save your panels also to your HD.