What, exactly, is actually producing that output?
It isn't the SHT11 on its own, is it?

As Craig says, you need to narrow this down to determine whether the fault lies in your basic reading from the sensor, or in convering the data for output, or in the output - or some combination.

The code you supplied is from Sensirion - so have you asked them about their code?

I note that the code uses a 'C' delay loop, which is always a Really Bad Idea - are you sure that all your compiler settings, clock frequency, etc, are correct to give the required delays?