I had exactly the same -- accumulating problem with my overclocked (to 60Mhz) CS MkII also in an A4000T. Finally it just gave up.
I sent it off to Jean Jacques in France at
www.amiga.fr and got it back working perfectly 2 1/2 weeks later.
He blames overclocking which I accept - the CPU is robust but other parts on the card may not be. Could even be normal 'end of life'.
Good Luck.
