First off if you are getting Account Offline, go to “Menu / File” and see if it has a check next to Work Offline. If it does click it and close and reopen eM Client.
SQ Lite error 10 disk i/o error could be a corrupted database or possibly a corrupted account or possibly a physical error on the harddisk.
So first i could try “closing eM Client” and then manually running the repair in the dos prompt or terminal depending on if you have Windows or Mac and see if that fixes the problem.
To Repair eM Client for PC or Mac via the prompt see this link from Gary
https://forum.emclient.com/t/em-client-stops-working-when-accessing-some-local-folders/93066/2
If repairing the database doesn’t fix the problem, then if you have been making regular eM Backups either automatically via the Settings or manually via the Menu, then try restoring a recent dated backup when you know you didn’t have that error via “Menu / File / Restore”. Any new mail since the backup will update when eM Client reconnects,
Or if you don’t have any recent eM Backups, then if you have IMAP, Exchange, Office 365 or iCloud accounts, go to “Menu / Accounts” and try removing and readding those problem accounts and see if that fixes it.
Next if removing and readding those accounts still doesn’t fix it, then “close eM Client” and go to the following eM Client hidden database folder and “rename it to eg: eM Client-Old”. Then reopen eM Client and setup as new and see if that fixes it.
(Windows hidden eM Client database folder)
“Users\yourusername\AppData\Roaming\eM Client”
(Mac Hidden hidden eM Client database folder)
“Users\yourusername\Library\Application Support\eM Client”
Lastly if a brand new database still doesn’t fix it, then you may have a eg: physical internal disk problem and might need to run some tests on your drive.