Workgroup vs. Homegroup:
I initially was using Homegroups (Windows 7 and Windows 8 machines). Then, it told me it can't share the root of a drive. So I disabled homegroups and now use normal file sharing.
While I share 40hz's dim/purist view of homegroups ... Their purpose is to step around the issue of having to match credential between machines in a workgroup (a.k.a. the pinnacle of Administrative overhead oriented nightmares). Homegroups have a singular key that is shared between all member machines allowing access regardless of logged on user's existence on the target machine.
Never share the root of C:, it's horribly bad form and make BOFH's cringe, wince, and frequently homicidal.
Note: the professional version of any Windows client OS (workgroup or domain) will have a hidden administrative access only share called C$ if need be. Creating another one is just begging for disaster.
Some folders share, some don't:
Some folders from the same computer get shared properly, I can see it from the other and access it no problem. Others don't. Same permissions, same everything. The one that doesn't work is a root drive, but I don't understand why that doesn't work.
They have literally written books about this one; file permissions vs. share permissions. You'll need both to get write access to a Windows share.
On some folders, I have full control for all users (everyone, administrators, guest). Yet when I connect it is read only. So whether someone has full control or read only...it really only works in read only. I don't understand this.
Rule of thumb 101: Never grant Full control to anything for any reason...ever. Seriously, this is another 5 star bid for tragic consequences.
Always administer shares from their own hosted root.
Share permissions need only Change for Users.
NTFS (file) permissions need only Modify for Users.
By users I mean only the specific ones that are to be allowed access to said share.
Full Control permission grant the ability to create shares inside of an existing share, and/or the ability to modify file permissions inside a target share. Both have ended badly every single time I've seen it ... Possibly due to the fact that this perilous configuration had much to do with why I got called there to start with...