Problem with export to STL

I have problem with export to STL. When model is done, I click on export option. When I choose Printing as STL - window is open with place to name, without type of file. The place is empty and I cannot choose type STL.When i type only name with .stl or only name - efect is this same - Error message - Problem with printing file STL. I.m remove DSM twice, cleaning registry and reinstall, but problem still exist. Without export to STL this program is worth nothing to me - because i cannot print nothig from my sketch