There's just a minor error in the TLK file, a stray "4" somehow found its way onto the end of the spell's name. Sending (or "Sending4" as it is now known in legends across the realm) is working properly, I just logged in to test it. The message always appears above your own PC/in your own chat log, this is normal, the other person is still receiving it if you formatted it correctly as shown here:
Every bug you described is normal. For the party invite GUI to appear you need to reactivate some UI option or something, it happens to everybody.
Not being able to select the box happens to everybody too. You just have to keep clicking until you can select it, sometimes it takes 8-10 clicks or more.
All characters default to Pick Lock on doors.
Sometimes NPCs turn hostile and attack you, usually because you've done something that the game thinks should flag you hostile towards that faction (it's a strange bug, but it happens).
NWN2 is an 11-year old game and most of our systems are highly customized (and in some cases held together with duct tape and barbed wire). You just need to be patient, these bugs are all common (except for the spell casting failure thing, and honestly depending on when that happened this morning it very well may have been after I did a live script dump into the module shortly before resetting it.)