Not allowed to save this file

Hello, I'm new in this world and also a new user of sketchup. So I drawned something in sketchup and wanted a STL-file. Downoaded the converter and tried to save it as :::: in program files/Sketchup/tools, but got as answer: you're not allowed..... I'm the only user and owner of the deswktop! (windows 8) Maybe somone?? Thanks,  Gerrit