This is quite a messy bug, seems to be related to many of the other problems people are experiencing. I'll try and get this fixed by 0.04 :)

This is a known issue, seems to only happen on mac. Which OS are you using?

This is now fixed in 0.04. You can cancel either by selecting another node on the right, or by right clicking in the node view :)

Hm. Did you move the ShaderForge folder after you installed it for the first time?

Scary! Did you delete the entire plugin and just reinstalled it?

It's lacking any error handling whatsoever at the moment, and this is one of the things that is needed! The one issue with coloring the connection red is that it's now sort of dedicated to indicate output channel. I guess another minor issue is that if you indicate things are missing as soon as you create the node, it feels a bit, odd, that it basically tells you you did something wrong just by creating a node that is inevitably missing inputs.

I think I'll go with an error icon next to the inputs, that appear after you've started connecting it :)