Cubase 5 missing ports and missing all VST's

I opened a project that i worked on yesterday and suddenly this happens.
after i click ok it offers me to remove tracks and whatever i click tracks stay where they are but cannot be heard because all VST’s that were active in vst instruments now are gone.
Why cubase cannot load saved VST’s? other projects are working fine and in this project i was opening tracks and vst’s just like i always do.