Steps to reproduce:
1) Create Host (with interface)
2) Create discovery rule with parameters:
Name - drule1
Type - Zabbix agent
Key - vfs.file.contents[/path/to/file/Discovery2.txt] (file attached)
3) Create Host prototype with parameters:
Name - host_{#KEY}
host groups - any.
4) Turn on server and agent.
5) Check discovery list page info column.

Result_1:
Error message appears

6) Navigate to host list page.

Result_2:
Host discovered and created

Expected:
No error message, host created.