In my case, it's actually saving the file, which is why I have to overwrite it. But Bridge also won't preview the file (it has a generic PSD icon), until I save again. And the folders DO have proper permissions. It will save from PS to the same exact folder without a quibble sometimes, and as I said, occasionally not other times.
It might not be the same thing, but I have to wonder if it's related. It just happened to me yesterday, in fact, but it's been several weeks since the last time it happened.
So it's rather an Adobe problem ...
2. I believe this is a Photoshop permissions issue, that should not exist. However, this seems to be a workaround. From Bridge select your image and in the shortcut menu consistently use "Open With" and choose photoshop. Do not use "Open." Do not double click. This seems to bypass Photoshop permissions and you should be able to save your changes to the server.
3. It shouldn't be this complicated. I do not believe that the "we do not support working to a server" mantra is valid. This should be fixed by Adobe.
In my testing I have found that I can save PSD files if I have all Finder Windows closed before starting up Photoshop and I open the PSD file through the Photoshop file browser. If I open a Finder window while PS is open I get the can't save error. This method works most of the time. I have not determined what the issue is when it does not, but will post an update if I do.