Can you tell me what you were doing when you got this error? And/or where you see it?

Peter: Could you answer comment 1, please?

Petr: ping

I don't remember what I was doing, but I know that everytime something break it just say "Failed" or Error

That isn't very descriptive error.

Example: try to add user to a project while it already is there the error message should be:

Unable to add user to the project, because they are already member of that project

instead of:

Failed.

I got this today.

add a security rule to a group with a missing or wrong parameter. (e.g. i think i had CIDR of 0.0.0.0.0/0)

It's not useful to have a bug that describes a general category of bugs -- might as well just have a bug that says 'make interface better'.

I welcome specific bugs, though!