proteus excessive CPU load error

[choi]

I don't know what's wrong with this circuit.
I get an error when I click the button







after pressing the button

 

[Harald Kapp]

Looks like the computing requirements to simulate this cirecuit in real time are too much for your CPU. The simulation should proceed, but at a slower speed.

I see some issues with the circuit:

• Using U1:C and U1: D with linear feedback is a technique sometimes seen but this technique uses the 4069 out of specs in an anlalog way. This may cause issues with the simulation, but honestly I don't know how Proteus handles this.
• Pin 5 of the NE555 typically requires a 100 nF buffer capacitor to ground. The modern CMOS versions are more tolerant. Again, I don't know how Proteus handles this. But adding the capacitor won't hurt.
• What's the use of D13? There's no power source to feed back into the battery. This diode can as well be removed.
• The clock input of U2 is permanently at ground potential:
  
  Turning on Q2 doesn'T change that. I think you want to connect the clock input to the collector of Q2, not the emitter?