Ok, I started thinking about this and both times I had the problem I was using the same lens. I played around with that lens on this afternoon and experienced a problem with focus and shutter speed. I cleaned the contacts of the lens and it is now working perfectly.
I am crossing my fingers you maybe correct. I will be shooting my niece's graduation ceremony this weekend and I want to use the same lens; a Sigma 70-200 f2.8.