Modelsim Error: (vcom-7) Failed to open design unit file "..." in read mode

Dear all,

There is an error I need your suggestions:

Error: (vcom-7) Failed to open design unit file "directory/file name" in read mode. Can you inform me how I can overcome it?

I am using ModelSim Altera Starter 10.1d with Quartus II 13.1.

Thanks!