Any notes (as well as files) you save can be quickly accessed from the item itself in the center column. Just toggle the arrow to the left of the item to reveal any attached notes or files.
I got this error after installing the new beta version, 2.0. I decided to revert back to version 1.0 and uninstalled 2.0. When I installed version 1.0, that's when I got the error. Files that remain in your Firefox Profile from the 2.0 version cause this version error. The easiest way to get around this problem is to re-install version 2.0 again.
Zotero's fix: http://www.zotero.org/support/kb/newer_db_version
Not all databases work with Zotero. Use this add-on to grab formatted citations from LexisNexis.
The most important tip to offer about troubleshooting is to have you read Zotero's instructions on backing up your data. No matter what issues you have, if you understand how to create a backup, all will be well.
Additionally, Zotero offers a nice checklist of troubleshooting tips to try when all else fails: http://www.zotero.org/support/troubleshooting_translator_issues. Also, you can report your troubles to Zotero:
First, locate which version of Zotero are you using. To locate this, click on the “gear” button and choose “about Zotero”
Next, Try to add a new citation to Zotero or try to do whatever it is that's causing the problem. Right after you do this and the citation disappears, click on the gear button again and choose
The window should include information about the problem, click next and submit the information to Zotero. The resulting window will provide you with a reporting code/number. You can either register at Zotero Forums and log your problem yourself, or send this information to Jen Holman and she will log the problem on your behalf.
You must set Firefox to accept third-party cookies for Zotero to properaly save new items to your collections. To check if cookies are enabled, select Tools, Options, Privacy, Use custom setting for history: