Question: I was using underscoreGS for a long time, but I got "Library with identifier underscoreGS is missing (perhaps it was deleted, or you don't have read access?)" this error suddenly.

underscoreGS should be a public lib, I should be able to access it. I also try to delete and add this to the project again, I can re-add it, but the error still there.

This is my code

```
  if (tmpDate.getTime() == tomorrow.getTime() && underscoreGS._indexOf(added, row[1], false) < 0){

```

Does anyone have the same problem? Or underscoreGS having a problem?

Answer: 
I can reproduce this behaviour. It looks like this behaviour is not limited to `underscoreGS`, but others like `GSUnit` and `YouTubeApp` result in the same error message.

I'd say it's possible that the owner of these libraries has changed the sharing settings and these libraries might no longer be public.

This has been reported in Issue Tracker:

* [Issues with underscoreGS, GSUnit libraries, and others?](https://issuetracker.google.com/issues/176763313)
* [Error replacing library](https://issuetracker.google.com/issues/176760972)

### Update 2020-01-21:

One of these issues was updated with [the following comment](https://issuetracker.google.com/issues/176763313#comment9) from Google:

> 
> This is not an issue with library import, this is a configuration problem by the library host/owner.
> 
> 
> Please take this up with the third party developers of the affected libraries.
> 
> 
> 

So apparently, this is not an issue with the library import process, but with the libraries themselves. Since these libraries are not officially supported by Google, anyone affected by this should take this up with the library developers.

Also, another developer shared backup scripts for these libraries in [this comment](https://issuetracker.google.com/issues/176763313#comment5), as mentioned in [Gonzalo's answer](https://stackoverflow.com/a/65724148).

### Reference:

* [GAS Library Management (public)](https://sites.google.com/site/nnillixxsource/)
This is happening to me aswell just since yesterday for the ObjApp library but intermittently which makes me believe it is on Googles end