PCS7 trouble

I have PCS7 multiproject with 1 AS and 1 ES/OS stations. Nothing interesting, self-education only.
But I have a big trouble stopping me: OS is compiled without errors but cann't download WinCC application to the PC station. HW config of PC station downloaded without errors. My opinion: regardless of the fact that project is configured as single user, WinCC application wants to be downloaded to another (non-existing) PC. Compile and download wizard in Plant View says nothing about reason. Download in Component View says "No path to the runtime OS has been selected". Why?! When I want to assign the same PC as target PC, I cann't do it - PCS says "The path to the Target OS must point to different computer". But Single User setting assumes only one PC in project! My ES/OS defined as Maintenance Station - may be problem is there?
WinCC project can be started from WinCC explorer. But, of course, it don't read tags from PLC Sim. I think it don't talk with PC station drivers and with PLC Sim accordingly. And I cann't make following steps therefore...
IMHO, Simatic PC station concept can pretend to the height of stupidity award as esoteric delirium. Why we must to connect PC and PLC and to switch mode from simulation to real application through this back orifice, not through two mode buttons?

Maybe it's interesting for someone. Problem is solved. Thanks for mr. Mikhaylin from Siemens Russia.
1. If WinCC project is intended to run at the same PC where is designed, it hasn't need to download it.
2. My mistake was to use Named connection on MPI. PLC Sim doesn't support named connections. It assumes only pure MPI connections.