Android adb "Unable to open sync connection!"

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

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.