Suddenly, there is a problem importing MySQL file using phpmyadmin in user cpanel. But there is no problem if importing mysql file using root account via WHM link to phpMyadmin.

The problem is like this :
No data was received to import. Either no file name was submitted, or the file size exceeded the maximum size permitted [...]

If you found “DB Error: no such database” while opening Horde Webmail in CPanel, it seem that the horde database is lost. You can re-upload the table database or just do the simple way in Terminal

/scripts/fullhordereset

Yes that’s all, it will reset all your horde