Can't get rid of the infamous 006-0612 error on my 3DS...

[Frostwraith]

I have always played online with no problems on my 3DS. However, from a certain moment onward (about four or five months ago), the 3DS started giving the 006-0612 error and since then I was no longer able to play online.

I still can connect the 3DS for other things like eShop, SpotPass, Internet Browser... playing games online is where the problem is.

Other than the 006-0612 errors, I occasionally get the "an error occurred" error with no code, alongside the 006-0612's "cousins": 006-0614 and 006-0519.

What did I do first? Checked Nintendo's site on http://support.nintendo.com.

Here's what the site said about all three error codes:

The Nintendo 3DS is unable to connect to an Access Point. [...]

Connecting from a wireless home network:

• • Make sure that the Nintendo 3DS system is within 30 feet of the wireless access point and facing in its general direction.

• Make sure that any other interfering devices, such as microwaves and cordless phones, are turned off.

Couldn't have done nothing better than putting the 3DS right besides the router.
It didn't work. Error code 006-0612 all over again.

Tried to manually assign an IP address to the 3DS, tried putting it on DMZ, tried port forwarding...

Nothing works. Only on very rare occasions will the 3DS connect for an online match, usually giving time for no more than 5 matches, until it gives me the error with no code stating simply "an error has occurred."

I saw some claims about 3DS only accepting routers on channels 1 or 11. Tried that and it didn't work.

I have resetted the router to factory defaults and it still didn't work.

TL;DR version:
Got the 006-0612 out of a sudden.
Tried every solution I found on the Internet.
Nothing worked.

If anyone had this problem as well, I'd like to know about your experience.

Edit: forgot to mention that only this particular router is giving me problems. I've tried other routers (same brand too) and it worked fine. Also, the router I'm using is a Thomson TG784n.

Edit #2: Another occasional error I get is the 003-0499.

This is what Nintendo states on their support website:

Using a router:

• Check for wireless interference,which can affect the signal strength to the Nintendo 3DS. To help minimize wireless interference, try the following:
  • Make sure that the Nintendo 3DS is within 30 feet of the wireless access point and facing in its general direction.
  • Make sure that any other interfering devices, such as microwaves and cordless phones, are turned off.

Which once again, I've tried to put the 3DS close to the router and it didn't work.

 

[ndayday]

I realize you likely have googled this tons of times before but maybe thia will work since they are the exact same problem:
http://www.mariokartwii.com/f9/3ds-online-issues-error-006-0612-a-85580.html

Further on in that thread it also says to go to http://support.nintendo.com/ which you mentioned, enter error code 86420 and choose Wii-- different console obviously but apparently it works.

I know how annoying this **** is (used to get the aforementioned 86420 on Wii and had to try basically everything in that list), sorry if these are things you already tried.

 

[Frostwraith]

I know you're trying to help and I thank you for that, but I already did what you said. Checked those sites already, followed the instructions... and it worked for 2 KIU matches. Afterwards, it was 006-0612 errors all over again...

I really don't know what else should I do.

EDIT: I just have no words for this, honestly. When I insist on playing online, it has a very low chance of entering a room. The session doesn't last much though. Sometimes, I am in the waiting room in KIU and it disconnects me giving the generic "an error has occurred" message. This is very odd.