Nostalrius Begins - Quality wow vanilla realm (1.12)

Interface\FrameXML\MailFrame.lua:623: bad argument #1 to strupper (string expected, got nil)

This is the full name of error, it only started after latest server maintance. I'm not only one I see people talk about it in my guild aswel. I contacted ingame support but nothing helped I did everything as instructed by GM team but nothing worked so he told me to post it here. This error pops up when I try to send ingame email to one of my alts it's only tied to One character while others function just fine. Also same character that getts lua errors he got bugged friend list, which keeps disappearing and appearing thrown all over the place where it doesn't show people who are online and then offlined. Instead it's messed up totaly.

1. I reinstaled game- clean instal.
2. Tried to delete, WDB, WTF, Interface folders (yes after I deleted these I got ingame cinematic upon launching wow, including all of my keybinds and video settings has been resetted).

None of these worked, I see people complain about it even tho they do not have any addons instaled so this issue is not addon connected at all. I think it is server sided hence it only affects some characters while others work fine.

So any answer or help is great thank you.

This is 99% chance of being an addon conflict. But you are saying you did a clean install. hm.

In your friends list hit the delete friend even if you see anyone in there or not. Most likely someone has left the game that is in your list. deleting first character in there should make it visible again. (just re-add person afterwards).

The only other thing I got for you is, Is the toon you are sending all the mail to, picking the mail up?

I sent quite some items to disenchant on him but didn't pick them up yet? Hmm maybe that is causing it? I'll check report asap.

EDIT: Update.

Small update it still happens after clearing all the mailbox on alt. So it's still where my X character sends to any other character mail I get instant lua error as soon I start to type characters name. And as already noted it only happens on one character every other character functions just fine. I really don't get it whats wrong.

Update 3. Friend got same issue just with friend list not mailbox. Another guildie getting same lua errors.

Could it be that FrameXML text file is causing this error? Maybe it's missing some strings? But then again doesn't FrameXML only write down stuff that is being used by addons?

UPDATE 4. Sorry for spam and my apologies but I found what was causing the issue. It is actually tied to your friend list and not addons at all or any other interface based folder.

You remember that I said that my friend list was appearing and disappearing all the time. It has been rather bugged up. So I deleted every single friend in there, and when I started deleting it repeated several times that I removed same friend for 5 times. I guess for some reason it was over crowded by same character names. After I deleted every one of them I went to mailbox to send email again and there was no error!

tl;dr In short delete your friend list completely and it should fix this specific error. After that you can slowly add all of your friends again.