Projects Blank that Contain Map Markup

Initial observation of blank project problem:

For some reason all projects across all sites are now blank upon opening if the project is new or existing and contains markup.  By markup I mean an arrow, a rectangle, text, polygon etc.

There is nothing useful in the logs to indicate why this might be happening - debug mode is on.

If the project does not contain markup then the project seems to open without issues.

I upgraded to essentials 3.10.1 last week but 'downgrading' to 3.10 does not seem to fix  the problem.  Running silverlight viewer 1.6.

Any help with this problem would be much appreciated.

Regards,

Dion Liddell.