If you add new audio into a project, say the source is a folder on the syte,. maybe desktop.
 
if you use CTRL-S to save the project and then delete the source file, when you re-load the project it (SPLAT) says the audio is missing, even though a CTRL-S for the project was done.
 
However is you do a FILE -SAVE AS command instead it correctly saves the new audio into the audio folder of the project.

Is "Always Copy Imported Audio Files" checked in Preferences > File > Audio Data? If not, that could be the problem.

ahhh, nice one scook - hadn't thought of that - I'll check

Bingo! thx m8 problem sorted  ...(not that it was a real problem, ya know what I'm saying )