Measurement Unit: Correct

Hi everybody!

I opened up the file, then this error was showed  . How to fix  it?.
Since I changed the unit and opened a file then it showed this error .  I want to use units mm instead of the default  unit is feet. In order to open it the next time without error,please!

I use Prostructures SS8 version 08.11.14.195

Thank a lot.

It's my file Ex1.dgn