Many unexplained problems are directly related to this location. If you aren't aware as yet, it's pretty much universally recognized that the default install location used by Steam (to the "C:\Program Files" folder tree) is a problem area due to the anti-malware security measures taken with it since the release of Windows Vista.
3.7 Second Rule - Make it playable first.3.6 First Rule - Install one mod at a time.3.5 Adding third-party tools to mod managers.
3.3 Do NOT accept the default install location.