As a programmer, they offered me an upgrade as project manager, but my feeling is that I can have a more effective contribution in a technical role that in one administrative.

When should I accept the promotion?

Generally speaking, I think that people should do what they love and what they like to do, from the time you are offered a promotion to someone is because he has been doing a great job today, and certainly learn new things in the new position and obviously have a better financial remuneration, but if it really is something you do not like do not good that post. That's my opinion.