With those details, I think I know what happened. Most probably, although it's not completely necessary in order to result in this behavior, you installed ViEmu before VS.NET was ever run. The first time VS.NET is run it sets up all sorts of configuration tables from scratch. Also, the first time ViEmu is run it scans the active keybiding scheme for clashing keybindings and removes them, creating a new "ViEmu" keyboard scheme. Unfortunately, if both happen at the same time, it is possible that ViEmu will run before VS.NET's startup process (not because of multithreading issues, but because the startup sequence ordering is not well documented nor accessible). And, in this first scan, ViEmu will create the "ViEmu" keyboard scheme based on an empty list, thus resulting in a complete lack of keybindings (such as the assignments for the RETURN and BACKSPACE keys). This is only noticeable for these keys and in insert mode, because the behavior of most keys is implemented directly by ViEmu (RETURN in normal mode, etc...) or hardcoded in VS's editor (regular alphabetic keys in insert mode).
The reason I haven't fixed this is that it is very uncommon (although a few people have experienced this), not easy to fix (it's not easy to control the startup sequence), and I have developed a better method for "keybinding overriding" in ViEmu/Word+Outlook, which I plan to include in a future release of ViEmu/VS. This new method does not rely in modifying VS's keybindings at all, so it will be much simpler and will cause fewer hassles.
In any case, the steps to fix it in your configuration are the following:
1) Go to Tools|Options|Environment|Keyboard
2) Select the "ViEmu" keyboard scheme from the drop down
3) Click in the "Delete" button (answer yes to the msgbox)
4) Select the keybinding scheme you prefer (VC++ 2, VC++ 6, Visual Studio, etc...)
5) Select the ViEmu options page (Tools|ViEmu)
6) *Close* the options dialog (this will "flush" and apply all the changes behind the scenes)
7) Reopen Tools|Options, it should be in ViEmu as that's were you left it
8) Click in "Keyboard"
9) Click in "Forget" below the left list (answer yes to the confirmation msgbox)
10) Click in "Save & remove" under the right list (answer yes to the confirmation msgbox)
And close everything. It's a bit of a hassle, but that should leave you with a proper list of non-clashing keybindings, proper restoring of the original ones when Ctrl-Shift-Alt-V is used to toggle ViEmu on and off, etc... as I described above, I have plans (and code) for a much simpler system in the future, so this problem will disappear in future versions of ViEmu/VS.
Thanks for being so understanding and let me please apologize for the hassles again.