the error comes from the only card that is into MoBo, that is the same card where i've plugged in the HDMI.. so if that is the card connected to monitor, that must be GPU#0..right? in other words, GPU#0 is the card you use to connect monitor, is it true? if i see video output on monitor it means that card is the GPU#0
No, I don't think numbering has anything to do with connected display, GPU#0 is usually the card installed into the "main" pci-e x16 slot (in most cases the top slot), but sometimes the order changes in multi-gpu rigs. Install some monitoring app (like MSI AB), watch for "gpu tachometer" graph while stopping the fans on the cards with your finger.. that's what I do to find out gpu order in my rigs, then I label the cards and write down which card corresponds to which index in monitoring and mining software.