What version of SF-12 (Audio Studio of Pro) ? What format are you trying to save as? Have you tried a different folder? (your Documents folder in the main C:\ drive for instance)
FWIW, When uninstalling and re-installing, I recommend uninstalling using a third-party uninstaller like 'Revo Uninstall', that can remove the left-over registry entries and other pertinent data the OS uninstall leaves behind, which can cause an issue to reoccur.. Revo Uninstall has a pro and freeware versions. The free version is adequate in most cases,
In any case, welcome to the Magix Sound Forge users community @happymanth.