Is anyone able to help me?

I cannot. However I did some Googling, using queries and keywords similar to:
and much of what comes back, points to (a) problem with Win7 that was not present prior to Win7 (or maybe it was less apparent, I dunno), or (b) a bug in CIFS/Samba and/or the kernel (Yes, I'm being vague, because none of the results I found gave a concise description, because nobody seems to know precisely what's wrong).

There's also evidence that this situation has been around for some time, although I cannot say with certainty that *any* of the results I got from Google, describe your situation exactly -- but there are many very similar stories to be found.

I won't paste a bunch of the links here that I've been reading, because if you Google using the words I've suggested, you will find all the same pages I found. Using those keywords and Google (the second line of keywords was actually my first, and most productive search), read the top 10-15 results; I mean, open ALL of the top 10 or 15 results you get on Google, and read every thread from top to bottom. You will see some suggestions of two or three (or more) Windows registry keys that you need to modify or create, which do various things to permissions, compatibility levels, etc... You will see suggestions about removing (uninstalling!) some Windows services/applications which seem to "interfere" with networking; examples included "Windows Live Messenger Service" and "Windows ID Credential something-or-other. There are lots of other ideas too, about CIFS and Samba and "it worked before I did foo, but now it's bar.", but I can't remember them all.

Anyhow, NONE of the above that I have written, nor any thread you find using my suggested keywords, is guaranteed to fix this problem. We don't know with any certainty what the problem is yet. And it's pretty much gotta be YOU that discovers what the problem is, where it's coming from, etc.. It's "looking like" a Windows-originated problem to me, but as I said, I don't use Win any more and am totally speculating.

More testing suggestions (forgive me if I repeat something already done earlier):

1) Can you connect & share the shares from another Win machine? No problem?
2) What about from a different Linux? Maybe a LiveCD? Have you tried one or more other perhaps older AND newer Linux kernel versions?
3) Have you manually inspected all cables, connectors and hardware for damage?
4) how about using a different NIC on either end of the connection?
5) Google various of the error messages you get on the Linux end - just pick and choose error messages and stick em into Google.

That's all I have to offer. I wish you luck - I know how frustrating these mysterious problems are, and how difficult it can be to find answers when one really doesn't know precisely what to search for.

Kind regards!

Wow that's amazing. Thank you - didn't even think (doh!) to check for more generic issues.

I'm trying some of these changes. Not even sure where to go with this but I'm looking to try anything at this point.

Wow, so I *think* I figured this out. I think the only thing I needed to was change my mount options. "noserverino" seems to be what is doing it for me. I didn't see that as an option (and tried the few other Windows 7 registry hacks) but I'm happy... I think it's finally working.

Thank you for your help, and you especially, GrapefruiTgirl - that was really kind of you!

Awesome!

The `no serverino` option, as best I can tell from my reading yesterday, is a workaround for a known "situation" (a bug, a glitch, whatever). Ideally, they will fix it and that option will then go away.
I didn't suggest it specifically (after reading it yesterday) because it did not seem to be described as a workaround for a problem matching YOUR exact problem.

Either way, I am very happy that it does seem to work for you! Keep us posted if this situation changes or improves in the future. Meanwhile, I'll leave it up to you to decide if/when to mark the thread [SOLVED] (OOPS - I see you have already - good stuff!)

Kind regards.

Still seems to be working!