"Cannot connect systems with different fluids" when trying to manually place pipe. Bot can place pipe fine.

[FenixLilly]

When trying to place a pipe manually, it fails with "Cannot connect systems with different fluids". There is no issue with placing with a bot, however. There are no different fluids so it should work. Flamethrower system had only crude oil in it. This has happened before but I couldn't replicate it until now. Save file ready to show the issue and screenshot attached.

[Silari]

You've got heavy oil pipes from refineries feeding into your crude oil system. Probably from before you switched fluids.

They're off due to no heavy oil for the cracking but their fluid boxes are still connected.

Might be some others but those I found.

[FenixLilly]

Thank you, I will look into that. Is it not still strange that it lets a bot place it but not the engineer, manually?

[aka13]

Thank you, I will look into that. Is it not still strange that it lets a bot place it but not the engineer, manually?

The bot is more or less an override mechanic for complex setups, where such mixing is deliberate.
In the old days vacating the pipes was really tiresome, and the mix check got introduced, which prevented a lot of unwanted situations.
At the same time, it would not always do what the user intends to do, so the override via the ghost exists.