Can't Build or Run when using other mods

So I am making a mod that is an addon for a few other mods, but when I try to build my mod, I get an error for every API , basically saying that the website used to get the mods (modmaven I think) doesn't exist, or at least can't be connected to, but I was able to find the website by searching for it, and it worked last night.

Additional problem: when I get the error, MCreator is locked up, so I can't scroll the console to see all of the errors, nor click on anything, and when I try to refresh the window, the window goes blank, whicha results in a problem with me forgetting the error, and being unable to find the logs for the console, if they exist.