I purchased Seo Pro mod on 2012. Can I use it on another forum of  another website?

No mate, as our license states you can:

9. Each license is attached to one (1) domain, if you need to change it please contact us, but keep in mind you can only change the domain of a license one (1) time and you can do it only if the purchase was made less than 6 months ago.

In this case you need to get a new license for that website.