Q: Please sign in again.  iTunes Match has encountered an error.

This continues to happen on my Windows and Mac machines.  I've followed the step-by-step instructions given here and they only seem to help for a week or so and then this message crops back up.  Very frusterating.  Other users report not having this issue.  The fact that I'm having it across all my machines while others say they don't have any problem leads me to believe that the issue is actually on Apple's side with how they handle their accounts than on the iTunes side.  Just a guess though.

I sure hope with the release of iTunes 11 this bug is squashed.

And the weeks roll by with no solution, or even a comment by Apple iTunes Support Crew.  They are still hiding in the bushes and that makes me mad.

I paid for iTunes Match and you (Apple iTunes Tech Support) did not deliver your part of the bargain. You should have said, "Please buy this software although we are compeled to tell you that it is buggy and does not work all the time."

For me, I solved my iTunes Match problem by running iTunes as Administrator. I even right-clicked the iTunes.exe file in the C:\Program Files (x86)\iTunes directory and clicked Properties, then the Compatibility tab and chose "Run this program as an administrator" so now every time I run it, it runs as Administrator.

However, the problem came up that Windows 8 did not see my music, stored on my Network Drive. So, I had to edit the Registry to get Windows 8 to see it. Apparently, in Administrator mode, Windows 8 does not see network drives. How to fix this was found here: http://www.winability.com/how-to-make-elevated-programs-recognize-network-drives /

Good luck to all! My iTunes Match now works fine.

Walt D in LV

Sorry, no solutions to offer, just another me too post.  This only happens on the computer where my music originally lied.  All other computers I add with match work seemlessly.  Makes me tempted to detele my entire itunes library from my orig mac and then just start again

I'm having the exact same experience as mic50: my home Mac (MacBook Pro 15-inch late 2012 OS X 10.8.2 iTunes 11.0.2) has this issue every time I open iTunes; however, my work Mac (MBP 13-inch 2011 10.8.2 11.0.2) never has this issue.  Before getting iTunes Match I basically duplicated my original iTunes library on an external drive and brought that to work.  Since subscribing I've been using Match to keep both libraries up to date.  It makes no sense to me that the work computer has no issues, unless it has something to do with the Internet connection at work being so much faster and more stable.  My home Internet is pretty decent, though. 

Another "me too" post. Using MacBook Pro 15" late 2011 with OS X 10.8.3 and latest iTunes. Everytime a start iTunes the error message "Please sign in again" appears. When I do this, the iTunes library updates correctly in iTunes Match. But the next day I have the same problem again: always the little cloud with the bolt in the middle.

I thought that maybe the network connection to the iTunes Store did not work, so I disabled Little Snitch: did not solve the problem. Next I rebuilt a new iTunes DB Index (iTunes Library.itl): did not solve the problem.

I am getting really frustrated now.

SAME THING HERE.   iTunes Match keeps asking me to add the computer every frackin time I open itunes.   This is such unorganized BS.   I keep seeing the issue and others like it all over the internet.   And not a frackin word from Apple.    its just so annoying why is it up to user forums to bang out this issue?      

TESTING 1..2..3... APPLE IS ANYONE HOME?  

I am becoming more and more convinced that Apple will soon crumble under its lack of vision and lack of consistent high standards for delivering an exceptional user experience.   For many years Apple had a solid track record of just being stellar, plug and play, it just works as was often the case when Steve Jobs was around.   Seems that all that is going on these days at Apple is slightly improving on things that Steve Jobs created.    So the iPhone is thinner, iMac is thinner, maybe there will be an iWatch in the future (which again I am sure Steve Jobs set into motion).   

The iCloud was one of Mr. Job's last projects according to his biography.   Apparently he was so upset at the poor reviews the mobile me service was getting he threw a tantrum and declared it had to be fixed.   iTunes match was also elluded to in the book, an amazing cloud based music hub that would have literally all music pushed from the cloud, Steve's vision was certainly awesome, but again here we are with the lack of being able to make it happen. And no one at Apple is even seeming to acknowledge the issue. 

Apple's makin cider with the left overs, soon the tree will be barren... 

Did you try this fix?

"...running iTunes as Administrator. I even right-clicked the iTunes.exe file in the C:\Program Files (x86)\iTunes directory and clicked Properties, then the Compatibility tab and chose "Run this program as an administrator" so now every time I run it, it runs as Administrator"

This stopped the issue for me.

Also i am  sticking with itunes 10 which seems much less buggy

Another "me too". Since i delete the "itunes store cache" before closing itunes (itunes settings/extended settings), imatch works fine. First of all, you have to restart itunes match (alt-close itunes match). Try it out...

Additional information: the check box "itunes in the cloud purchases" must allways be marked (itunes settings/store). Sometimes the mark will disappear and then imatch doesn't work anymore.

I don't know, if this is the solution or in a combination with my post above (store cash re-setting). Anyway, my itunes match works fine...

bird_y, are you running 10 or 11 ?

I wanted to try to delete the cache that you mentioned but i don't see where those settings are that you describe, maybe because i am on windows using itunes 10?

Mine works good for now but I want to see if i can disable the Admin setting for itunes and still have match working properly.

Why don't you want to run in admin?  If it works like that, just stay in evacuated privileges for that app.  Sure…it's an extra click of the mouse, but after several updates with no cure in sight, who cares.  Now, if you're on a limited PC (in which case, you're not an admin for your profile), that's another issue altogether.

Leave it to autocorrect:

I meant "ELEVATED" privileges, not evacuated privileges.

It's because the pop ups are driving me crazy, every time I start itunes, or import a disc, or  whenever Match does anything at all (updates) it asks me if I want to allow the program to make changes... and I dont know how to remove that pop up except to reduce security settings which doesn't seem safe... pop up windows over and over and over... very frustrating it seems there has to be another way?   I guess if there isn't then I have to just deal with it but it is driving me nuts

Oh, well that's a different issue then.  Once you open iTunes as an admin, it's given an elevated security token.  At that point, you should no longer see any prompts for admin activities in iTunes.  Importing CDs shouldn't require admin at all, unless you've changed the rip location to a folder outside your user profile directory.  In other words, the idea is to launch iTunes, click Continue (for elevated privileges), and that's it - for that running instance of iTunes.