Pro tools 1st project hard fail to download error msg
 

I have a project ive been working on for a while. It saved no problem before but yesterday when i tried to open it it has a yellow triangle icon next to the name. Pro tools first says it cant find the file. And wont open it to play. Please help! I really dont want to have to redo the whole session. How can i get a bavk up or to get the file to open no problem again??