Precondition: you need to have an exported file with a host saved on your computer

Steps to reproduce:

1. Data collection -> Hosts
2. Click "Import"
3. Choose a file that you've previously exported from host list that is stored on your computer
4. Delete the file containing a host from your computer
5. Click "Import"

Result: error message with text "Unexpected server error." is displayed, which is misleading for the user

Expected result: it should be possible for the user to understand what exactly is wrong from the text of the error message.

Reproducible in all places where some kind of import is possible - Hosts, Templates, Maps, Media types, Images

In Images the behaviour until 8.0 (before inline validation with ZBXNEXT-9752 is introduced) is different - after clicking Add for the new image entry the result looks like this: