Hello OverKnight...
Have you tryed to copy your PT 2005 license to the root of the PT 2006 folder?
Also try to copy your license file to your desktop, then press F8 and press 'Auto Find new License'.
This should find a valide license file.
If this not works, i sugest to contact Macecraft support, and ask if you are entiteld to an free upgrade or if you have to pay a small fee.
About the usage of the license i sugest to check the following Licensing Page.
Here you can find more information about licensing of the products from Macecraft.
Hope this will help you.