Latest update is unstable
Following the latest update of Zotero it seems to have become very unstable and it takes rarely more than one two input actions to crash. For example when I try to add a new entry from a PDF as "stored copy of file" Zotero first freezs for a few seconds and then tells me that I have to restart (error report codes 1178093087 from Standalone version and 603332634 from Firefox plugin).
This is a pity, because it used to work just great!
This is a pity, because it used to work just great!
But your problem is likely unrelated to the Zotero version anyway. Upgrade to the latest version and then check your database integrity in the Advanced -> Files and Folders pane of the Zotero preferences.
I am actually running the latest (4.0.12) version of Zotero in Firefox, but you are right that the standalone version was older. I have upgraded in the meantime to 4.0.11 which seems to be the newest one I am being offered.
At any rate I ran the integrity check on the database and it seemed indeed corrupted. So I followed the instructions at https://www.zotero.org/utils/dbfix/manual to repair the SQL database and then restarted the standalone Zotero. When I checked for database integrity it still showed it to be corrupted but this time it offered the option to try and repair it. After I did that another database integrity check was positive.
So my problem seems to be solved now, but wouldn't it be better to offer the repair option right away when the NS_ERROR_STORAGE_CONSTRAINT error occurs?