Q: iTunes Error 11503, solution anyone?

I'm also getting the same error.

I have the same problem.

When I've tride logging out I can't loggin back in.

OS X 10.8.5 64bits

iTunes 11.1

I have the same probrem.

I logout/in on itunes and select "account", it will be blank.

Itunes indicate "503 Service Unavailable HTTP/1.0" .

It must be network trouble ? But iphone updates apps normaly....

From Japan .

I try login again. So it works normally.

Updating apps are fine.

Same problem in the Dutch iTunes store.

Since I updated to the latest version yesterday, I'm now seeing this all the time (no other changes have been made).

Here's a possible fix for Error 11503 and for error 50.

It worked for me and hopefully it will work for you.

I believe this error is caused by the incomplete downloading of either an update to an app, or perhaps a big music file. In my case it was caused by closing the lid on my laptop when I was downloading app updates on a very slow internet connection in a hotel.

Anyway, here is what I did that fixed it completely.

Close iTunes.

Go to this folder : /iTunes/Mobile Applications/Downloads

You'll find tmp files there. Drag them out of this folder to a temporary folder on your desktop. The Downloads folder should now be empty.

Restart iTunes.

All should be fine.

If it's not, then I can't help further, but that's what worked for me.

Yesterday I was able to download again. I hope it stays that way. I hope it goes back to normal for the ones who are still getting this error.

Seems to work !

Thank

11503 is alive and well in 2016.

I tried the MS DOS routine - reboot (log out, quit the app, start the app, log in) tonight and was able to download.  I hope it lasts and I will try the reboot thing in the future and hope it works.  I guess that is why they call it "an unknown error", after all these years...

Somehow this seems to be linked to an AOL account authorization problem, even if you don't use the aol account with iTunes!

I'm on Mac os 10.11.5 and I've had an AOL account since pre-internet days dial-up.  My AOL account is not connected with iTunes in any way. 

My MBP has been getting a popup for the correct AOL account password.  I went to aol.com, signed in, and added a mobile phone number.

Now I no longer get the popup for the password, and iTunes no longer throws the 11503 error.  Go figure!

The "MS-DOS Routine" worked for me, thanks.