Also available in this thread on Quora.
I have encountered this problem far too many times and I have managed to narrow down my issues with non working auto-complete to a problem with running several Google Apps domains (and most likely with a second regular (non-apps) gmail account aswell). Here’s the skinny:
- If logged in to docs.domain1.com and from there accessing Google Docs I can enter a document and it will auto-complete my contact emails just fine when I select the share menu.
- If I then log into docs.domain2.com and enter a document the auto-complete from the share menu is completely dead, nothing happens when typing the first, second or third letter of the name. It still works on domain1.com.
- Closing domain1.com will not make it work in domain2.com, I have to close the browser entirely and then start up a new instance of the browser to access domain2.com, after that it works.
NOTE: In Google Chrome it didn’t even help opening up a new instance of the browser, the old instance had to be shut down first. In Firefox it worked opening up a new instance of the browser to access domain2.com with working auto-complete.
Hope this helps you to work around this issue aswell!