Google Drive Page Not Found - Sorry, unable to open the file at this time

I think you are logged in with two gmail account: That is why (/u/1,/u/0) may have been appended to script address (may be a bug).

So what you have to do is remove /u/0 or whatever is appended.

ForExample:

https://script.google.com/macros/u/1/s/ffffsdds/exec becomes https://script.google.com/macros/s/ffffsdds/exec

I have several Gmail accounts open at once and kept having this problem. I found it helped to close the Drive window, log out of the email account related to it, and then log back into the Gmail account and open Drive again.