Help! All VSTs have disappeared (Not Solved, but issue is resolved, no further panic)

I've just scanned VSTs to install the Ozone imager and I have now list all VSTs in the projects and the vst manager. The actual files are still present in their folders, and i've re-scanend,  but when loading a project I have a message that all VSTs are not available including dimensions  pro, Addictive drums, TH3 etc. . Is there a quick fix to this? I'm hoping this doesn't mean I have to go through all projects and manually rebuild all the settings.
 
Jerry
 
EDIT -four hours later)
Strange: I've just rebooted and the issue is corrected; the VSTs are present and projects open correctly with all VSTs present. A great relief, but I don't understand what happened!