ROBLOX Replication: Can't create default object of type workspace?

What does this error mean and how can I overcome it? This error happens whenever a player joins.

EDIT: All scripting work fine when testing but in an actual server they brake?

This does not appear to cause any harm to servers. And I am getting this error in all of my places, even if I haven’t opened them in studio for months.

Okay, but suddenly a frame has just disappeared when testing in a server and my sliding doors that use also use LocalScripts no longer work in a server. However the work when Playing with a player test option. The localscripts don’t work in an actual game server either. It’s really annoying cause it’s only just started happening.