EM client crashed when i change from Mail Inbox to calendar
with the symbol in the lower left corner
Could be that eM Client program is possibly corrupted in some way and needs removing and re-installing again.
So first backup eM Client via the “Menu / Backup”. You can see when the backup is completed via “Menu / Operations”.
Then uninstall eM Client and “Don’t delete the database” when asked on uninstall. Then reinstall the same or later version from the release history page and reboot, and then see if that fixes it.
If still the same problem, it could be there is some other program installed maybe running in the background possibly interfering with eM Client when you click between the sections.
Programs that can interfere with mail clients are things like eg:- Optional Firewalls / Security programs or Optional Antivirus programs , Optional Malware programs etc. So if you have any optional programs like that, try completely disabling those to test.
Failing that try disabling all background non OS related programs in the startup of your computer and reboot and see if eM Client then works ok. If it then does, you know it’s one of those programs and you will need to then enable them one at a time and reboot inbetween till you find which background program is causing it to happen.