How to generate a html coverage using *.cvt file?

I am trying to use 'cvsim' to simulate the cvt file and then 'cvhtml' to generate the html file.

While doing cvsim, i am getting the error as 'The related model must be open while coverage simulation is executed'. But the model is opened and the coverage file and model is in the same folder.

Is there any other way to create a html coverage report from the 'cvt' file?