Socket: bind failed on loading any project

Any time I load a project I get the following error in the console:

Code (csharp):

1. Socket: bind failed, error: An attempt was made to access a socket in a way forbidden by its access permissions. (0)

On Googling it, it appears to be an old error that was fixed a while ago, but there must have been a regression or something because I'm seeing it on 5.3.3p2 now.