Filipe, it means that your SSVM is unable access location where is your .iso file. 

Where is your http server on which you have .iso file? is it in remote network or is in the same network your SSVM is? 

Radek.

There is a known issue in current releases of CCP 4.x where you cannot delete failed templates/ISO's, this is fixed from CCP 4.2.1-3 or CCP 4.3 release onwards.

Meanwhile  Workaround via DB hack:

mysql> select * from cloud.template_view
<- Make sure the name of ISO template you want to delete from GUI, and check the Template_ID for that.

mysql> select * from cloud.template_store_ref where template_id=<Template_id>;
<- Verify the detail for the template id in template_store_ref

mysql> delete from cloud.template_store_ref where id=<id>;
<- Make sure you have to select the id of template_store_ref for that template

mysql> select * from cloud.template_zone_ref where template_id=<template_id>;
<- Verify the detail for the template id in template_zone_ref

mysql> update cloud.template_zone_ref set removed=now() where template_id=<template id>;
<- Mark the templates as removed in template_zone_ref

mysql> select * from cloud.vm_template where id=<id of template>;
<- Verify the detail for the template id in vm_template

mysql>update cloud.vm_template set removed=now() where id=<id of template>;
<- Mark the templates as removed in vm_template

and finally refresh GUI.