Bobs

Wow, that’s tricky to follow but I got there! Yes, it’s because throwing the right (wrong!) selection of switches connects voltage sources in parallel. As these are ‘perfect’ sources they have no internal resistance which means the simulator calculates the current flow to be voltage/zero=infinity current, which gives the error message. You can avoid this by always including a tiny resistor in series with each source, 1 milliOhm will do. Strictly you could often get away without doing this for EVERY source but sometimes it’s just easier to do it routinely to avoid this type of error message - a pain, but can save you hassle.

@Redstone_guy, you’ve deleted your comments to which I replied. Useful!

Sorry

:-)