4 months ago I installed in my PC the CS5.5
by dialing the serial number of the product I purchased in the boxes of the trial splash screen.
It seems like all the programs of the CS have been installed as purchased products
except for Fireworks (but I didn't find it out until now).
Now I need to use it and I am trying to install it from the trial version
(which I downloaded few months ago but had never launched)
by dialing my serial number but it doesn’t work.
I dialog says that my serial number is not valid for the product I am trying to install.
What is wrong with the license I purchased?
Sorry to have to tell you this, but you posted your issue in the wrong place. I know the forum is titled "Installation/Licensing", but it's not just a catch all for all Adobe products. It's for Installation/Licensing with only one specific product. Adobe Captivate.
Try clicking the link below and on the page that appears, click the drop-down selector and navigate to the forum that applies to your product(s).
And I'm assuming you have double-checked obvious things such as lower case l (L) where perhaps an upper case I or a digit 1 is expected? Others to watch for are using the digit 8 where a B is expected (and vice-versa) as well as the digit 0 for the upper case O (and vice-versa).
Cheers and best of luck to you in solving your issue! Rick