Hello @realx_x ,
I went through several posts, and in most cases the error happens because another instance of the editor is still running in the background, even if it’s not visibly open.
The main fix everyone recommends is to open the Task Manager and check for any leftover editor processes, close them, and then try saving again.
I’m also sharing the posts I found because they mention other possible solutions in case your issue isn’t related to duplicate instances.