Which extension are you trying to install?
It is a standard 3rd party extension (Floating Adjustments Panel) by the Roberto Bigano Group and I believe comes from the Adobe Photoshop Marketplace. The install file is an Adobe Zip Format Extension Package. My hardware setup is a Mac Pro running Snow Leopard.
Sorry to hear about the issue you are having. Did you try contacting the producer (Roberto)? Also did you get it from the Adobe Exchange panel or the Adobe exchange Classic website? I think by the sounds of things it may be the panel but the error message is strange as it's a free product with no licensing restrictions. Please let me know so we can try to figure out the cause of the issues.
Jonathan Ferman | Product Manager
Thanks for the follow up. I had originally tried to install the extension directly from a .zxp file sent by the developer. For some reason my valid serial number was not being recognized by Adobe. I solved the problem by using the Adobe Exchange panel and getting the extension from the Photoshop Marketplace. All is well now.
I'm the panel developer; I'm investigating the issue even though it looks quite strange because (unless something weird has happened) the ZXP you've got is the very same that is distributed through Exchange.
Jonathan, I'll keep you updated on the topic - please do the same if you happen to understand what could fire that licensing error. (by the way the package has been built with a Comodo certificate that will expire in October, so it shouldn't be a packaging problem).
Thanks for the response. I was able to install your Floating Adjustments Panel by downloading it through Adobe Exchange and it works perfectly now.