Loosing VST instruments connection

Hi all,
I am loosing the vst instruments in my midi project when I re-open the project.
I set up the instruments and connect them to the correct midi channels, etc.
Save the project.
Next time when I open the project, the sounds are still in the VST instruments list
but when |I play a track, it uses the “Grand Piano” as sound.
I am sure that I am doing something wrong or forget something to do,
but do not know what.
Can somebody help me out here??