First of all we’d like to pay your attention to the fact that trial version of Flash Optimizer is actually Shareware, which means you download the product and can use it to test the software. Still some of the features are truncated (saving the optimized SWFs in black and white for example). To get fully functional version you have to purchase registration key.
So, it is NOT possible that the SAME product stopped working after you have entered the registration key.
There are several possible reasons why it might seem so:
1) As you know the Demo saves the compressed SWF in B&W, so you might have referred to the file size of the SAVED file which can be smaller than the size of the file you actually get after optimization (in color). To know the actual size of the optimized SWF see the Information Box which pops up right after optimization is completed or use “SWF info” button.
2) ActionScript might seem corrupted after optimization. This problem can be encountered with both Demo and Full version optimizing the SWF files containing Preloaders, Intros or other AS. To fix the issue disable Scales compression.
3) The quality of pictures in optimized file is poor. This issue can be explained by the fact that images with bitmapped graphics are rather large and by reducing their size considerable you lose much of the quality. So, you have to experiment with the Quality/Size proportions in order to get the acceptable results. Demo allows you to evaluate the Pictures optimization.