How can I use a single license to register all my products?

To do this, you must use the same "License Hash" (from the Software panel). The License Hash is a big number which represents the seed to generate licenses for a specific Software. If two software have a different License Hash, the licenses generated for one software will not be valid for the other software.

To copy/paste the License Hash (to share the same license between different software), just right-click on the License Hash edit box and select Copy/Paste from clipboard.