Error while creating folder on webdav mapped drive of Sharepoint Online

Hi!

We have some sites on Sharepoint Online.

The site name is already in the trusted sites into the internet explorer. 

I map drives using this command line:

net use u: https://mycompany.sharepoint.com/sites/sitename/libraryname

Using windows explorer I can:

- create folders throgh web normally. 

- copy files and folders there.

- move file and folders there. 

But...

When trying to create a new folder named "A" in the root fo the library using Windows Explorer/Right Mouse click/New Folder, I get the following error:

"Rename Folder. The file name you specified is not valid or too long. Specify a different file name. " Options: Try Again | Cancel.

Note that I am creating, not renaming.

And more, I am creating a folder, not a file. 

If i click on "try Again", the error persists.

If I click in "Cancel" a folder named "New Folder" is created. 

Any Idea how to fix that?