Ok we have a good old System Error 53. 
Usually this is just a configuration issue.
- Are you using Windows Server 2008 or 2012
- Please install Desktop Experience and try again!
- Windows Server 2016
- Windows Server 2016 does not include WebDAV support by default. You need to activate the “WebDAV Redirector” Feature in your Server Manager console as described in this Microsoft support article.
- Otherwise
- Make sure, no anti virus software interferes with the connection from localhost to localhost on your Cryptomator port (defaults to 42427)
- Update Windows to the latest version. Maybe you have some pending Windows updates that would fix the issue.
- Please check the Windows Registry in
HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Control\NetworkProvider\Order. The keyProviderOrderneeds to have the valuewebclient. If it’s missing, please add it to the list (separated by a comma). See this blog post for more details.
- If nothing helps, see Microsoft’s WebDAV Troubleshooting Guide.