Hi, mac-
I believe it's a "permissions" issue of some sort...
I would suspect that it's either network or Safari related, probably at the system level. However, creating and testing in a new user account wouldn't hurt and might help confirm it's at system level, if it doesn't resolve it.
You might check your Network Preference Pane and turn off any proxies that may be enabled.
What are the specific permissions indicated when you do a Get Info on the Safari application?
You might also download and run
Onyx in automation mode and delete your caches. (You can use another cache cleaning utility if you already have one.)
Gary