Android adb "Unable to open sync connection!"

Question

I was having exactly the same problem, but I already had my phone connected to the computer's USB port. Sometimes disconnecting and reconnecting the cord worked but then it stopped working completely. However, disabling USB debugging on the phone and then re-enabling it has worked so far. Hopefully it keeps working! These fixes really seem like silly hacks.. I'm not sure what the underlying problem is.

I was able to clear this only by cycling the USB Debugging option on the phone.

This may also be related to a "too many open files" issue. I manually tried to install the app when getting the "sync" error above and that's when I got the "too many open files" clue. one brute workaround, based on some old posts, seems to be to restart the phone, and one google engineer suggested doing it twice, the second time before it goes into sleep mode the first time (details on why in the post).

That was a few years ago, and maybe they've fixed it, or just did some things to get around it in the usual cases and the reinstall-as-part-of-development is not a case that it addresses.

Nexus One here, CyanogenMod 7 (Android 2.3.7)... disable and reenable:

Settings > Applications > Development > USB debugging

And everything works now on Eclipse and Mac OS X 10.7.3.

I have been having the same problem when I have the phone connected through my keyboard's USB hub. IT went away when I connected straight to the computer's USB port.

I have had the same problem and restarting ADB wouldn't work for me. Sometimes rebooting my phone worked but not always, I was unable to program for about a week because of this glitch and I think I finally found a workaround! :-D

First of all, kill every program running on your phone. Having some kind of taskmanager makes this a quick task, otherwise you'll have to manually kill them all one at a time.

If that doesn't fix it, you will need to go to your phone settings, then go to "Applications", then go to "Running services", and kill every service in there. I'm using a Droid Incredible and I have yet to have this not work for me. :-)

So, the short answer is, kill all apps, and all services.

Also, keep in mind, you will need to close, and re-open eclipse to see if this fix has worked for you. I hope this works for you, I know it did for me! :-D