Dropbox 3.4.3 problem on OS X 10.7.5

README

Dropbox 3.4.3 on OS X 10.7.5 exits after few seconds with error in AuthenticationThread, tray icon disapears.
You can confirm by running this in Terminal.app:
  grep -h -A7 'Crashed Thread:' ~/Library/Logs/DiagnosticReports/Dropbox_*
output: lines of:
   Crashed Thread:  <SOME_NUMBER>  Dropbox::AuthenticationThread
   
   Exception Type:  EXC_CRASH (SIGABRT)
   Exception Codes: 0x0000000000000000, 0x0000000000000000
   
   Application Specific Information:
   objc[<SOME_NUMBER>]: garbage collection is OFF
   *** error for object 0xffffffff: pointer being freed was not allocated

========== Solution (until Dropbox releases fixed version; thanks: Reinhold K., Kurt G.): ============
1. (in "Activity Monitor" (it is inside Applications -> Utilities)): confirm no process named Dropbox is running 
2. (in Terminal.app): delete file dropbox-upgrade-3.4.3.tar.bz2 by running:
  rm <YOUR_DROPBOX_FOLDER>/.dropbox.cache/dropbox-upgrade-3.4.3.tar.bz2
3. (in Terminal.app): download package of some confirmed working version (here: 3.2.9), from https://www.dropbox.com servers:
 curl -L -o /tmp/Dropbox-darwin-update-3.2.9.tar.bz2 'https://www.dropbox.com/download?plat=mac&meta=1&build=3.2.9'
4. (optional) rename /Applications/Dropbox.app (for backup) purposes in Finder,
   or in Terminal.app by running:
    mv /Applications/Dropbox.app /Applications/Dropbox_3.4.3.app
5. (in Terminal.app) create folder /Applications/Dropbox.app/Contents:
    mkdir -p /Applications/Dropbox.app/Contents
6. (in Termninal.app) extract package downloaded in 3.:
  tar -C /Applications/Dropbox.app/Contents -xjf /tmp/Dropbox-darwin-update-3.2.9.tar.bz2
7. (in Termninal.app) set immutable flag for /Applications/Dropbox.app. Dropbox will be unable to upgrade itself:
  chflags -R uchg  /Applications/Dropbox.app

Now You can run Dropbox.app.

Undo by: 
1. (in Termninal.app) unset immutable flag for /Applications/Dropbox.app:
  chflags -R nouchg  /Applications/Dropbox.app

Now You can remove version 3.2.9 and rename backup You made in 4., or let 3.2.9 update itself automatically.

if Dropbox crashes again, run this:
grep Path: ~/Library/Logs/DiagnosticReports/Dropbox_*
If You get many lines like this:
/Users/USER/Library/Logs/DiagnosticReports/Dropbox_DATE_HOST.crash:Path: /Applications/Dropbox.app/Contents/MacOS/Dropbox
/Users/USER/Library/Logs/DiagnosticReports/Dropbox_DATE_HOST.crash:Path: /Applications/Dropbox.app/Contents/MacOS/Dropbox
and then some lines like this:
/Users/USER/Library/Logs/DiagnosticReports/Dropbox_DATE_HOST.crash:Path: /Users/USER/Library/Application Support/Dropbox/Dropbox.app/Contents/MacOS/Dropbox
it means Dropbox has managed to install updated and not working version 3.4.3 inside folder
/Users/USER/Library/Application Support/Dropbox

delete it, and make it immutable (will see, if it will help):
rm -r ~/Library/Application\ Support/Dropbox/Dropbox.app
chflags uchg ~/Library/Application\ Support/Dropbox

Undo after Dropbox fixes 3.4.3:
chflags nouchg ~/Library/Application\ Support/Dropbox

I have found one more little issue with Dropbox - AppleDouble files (with file names starting with "._", these are hidden in Finder.app under default settings) in /Library/DropboxHelperTools. It might or might not have anything with this crashing problem, but can be fixed by running (in Terminal.app):

sudo dot_clean /Library/DropboxHelperTools

(system password might be asked. Type Your password and press Enter. Letters of the password won't be displayed while typing)