RSSOwl problem: “Uncaught Exception. db40 engine closed”

My RSSOwl somehow got corrupted and I was not able to get it back to work, even after a reinstall of the software. The errors are:

“An internal error occurred during: “”. Uncaught Exception. db40 engine closed

“java.lang.ClassCastException” – “An error has occurred. See error log for more details. com.db4o.config.Entry cannot be cast to org.rssowl.core.persist.IFolderChild”

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So I started digging for a solution. I found out that the problem (in my case at least) was in the RSSOwl database file rssowl.db, which somehow got corrupted. RSSOwl is smart enough to create regular backups, which are to be found in files rssowl.db.backuprssowl.db.onlinebak and rssowl.db.onlinebak.weekly. These files are located at:

C:\Users\<your username>\.rssowl2\.metadata\.plugins\org.rssowl.core

I would suggest before doing anything else to create a backup of your entire .metadata folder (in case something goes wrong). Also make sure that RSSOwl is not running at this moment. So to solve the issue you can simply delete (or rename) the rssowl.db file and copy, for example, rssowl.db.onlinebak in its place. Fire up RSSOwl, and everything should be working as expected. 🙂

In case you for some reason do not have these extra backups, and/or you don’t care but just want to get RSSOwl to work, then simply delete the .metadata folder. RSSOwl will recreate all the necessary files and everything should be fine anyway. Note that in case you want only to save your subscriptions, the data is located in either of the following files:

C:\Users\<your username>\.rssowl2\backup.opml

C:\Users\<your username>\.rssowl2\backup_weekly.opml

You can backup these, delete the entire .metadata (or even the .rssowl2) folder, and then import the subscriptions from the .opml file in RSSOwl.