UK Residence card or EU Residence card?

Hi guys/gals,
I have a question that I didn't get a clear answer for from the UKBA site.
I have a Residence Card for the UK, valid until April 2012 but I moved, with my family to Slovakia in June last year. I now have a residence card for Slovakia.

The question I have:
I will have to travel to the UK for training as part of my job soon for 2 weeks.
How do I go about this?
Do I use the still-valid UK residence card or would the Slovak Residence card allow me entry?
Or... do I actually have to apply for a business visitors visa?
Oh... forgot to mention, I'm a South African Citizen.

I really don't want to get stuck at the gates.

Thank you in advance.