I have the same problem across my devices, PC, Mac and iPhone...

Sync account works! I press on TOOLS/SYNC i get this:

"Sync encountered an error while connecting:Incorrect account name or password. Please try again. [Preferences]"

I press Preferences and press update. Then I an able to 'update' my password, I put in the same password as before and sometimes it accepts it and show my 'sync preferences'. But in My browser I can't see the function activated, there is no icon, no notification... and when i press TOOLS/SYNC the same starts all over again.

"Sync encountered an error while connecting:Incorrect account name or password. Please try again. [Preferences]"...

Anyone?

Firefox 4: Windows 7

firefox home: iPhone 4.21

Firefox 4: MacBook OSX 10.6.5

I'm getting exactly the same problem here. Two fresh installs of Win7 on laptop & desktop, I've tried starting from each of them and both have the same problem. I've tried different email addresses and changed passwords... but I can log in to the web interface, just like the OP.

Come on guys, this is supposed to be out of beta now!!!

Fx4.0 I reset my account on Ubuntu and Windows 7. First sync appeared to work. After a couple hours, I'm noticing the 'Sync encountered an error while syncing: Unknown error...' notification again.

Same for me, I cannot believe all my bookmarks are gone! I am extremely disappointed in Firefox for the first time!

silverhawk184 -- Firefox Sync has been having lots of problems lately with their sever and many times it'll not sync. Most of the time, it'll get back to normal. You might want to wait a little bit longer (maybe till tomorrow) and see if it's back to normal.

I would recommend you do not depend on Firefox Sync completely. Use the following two add-ons as a standby:

http://www.xmarks.com/

https://lastpass.com/features_free.php

Friday 5/27/2011, it came back online. My phone (with a brand new rom) automatically synced to my laptop! I don't understand how that would work, but I like it!

I am running OSX 10.6.7 with latest update on MacBook Pro (2008). Even before I installed Firefox 4 Beta, something was wrong with Sync but at least it didn't keep popping up and annoying me to sync and then giving the error message.

Also running FireFox home on iPhone 4 with latest OS. Went through the routine with code, password, etc several times to no avail.

Would like to sync also with Windows 7.

Very frustrating!