Steps to reproduce:
1. Make a project folder the root of a drive for example: (e.g. E:\Assets\, E:\Library\, E:\Packages\, etc).
2. Open project

Expected: no errors are thrown
Actual: errors are thrown

Reproduced in: 2017.4.34f1, 2018.4.12f1, 2019.2.12f1, 2019.3.0b10, 2020.1.0a12

Errors (a lot of similar to these ones):
DirectoryNotFoundException: Could not find a part of the path "D:\Packages\com.unity.2d.sprite\Editor\UI\SpriteEditor\SpriteFrameModuleInspector.uxml".
System.IO.FileStream..ctor (System.String path, System.IO.FileMode mode, System.IO.FileAccess access, System.IO.FileShare share, System.Int32 bufferSize, System.Boolean anonymous, System.IO.FileOptions options) (at <437ba245d8404784b9fbab9b439ac908>:0)
System.IO.FileStream..ctor (System.String path, System.IO.FileMode mode, System.IO.FileAccess access, System.IO.FileShare share) (at <437ba245d8404784b9fbab9b439ac908>:0)
(wrapper remoting-invoke-with-check) System.IO.FileStream..ctor(string,System.IO.FileMode,System.IO.FileAccess,System.IO.FileShare)
System.IO.File.OpenRead (System.String path) (at <437ba245d8404784b9fbab9b439ac908>:0)
UnityEditor.UIElements.UXMLImporterImpl.ImportXml (System.String xmlPath, UnityEngine.UIElements.VisualTreeAsset& vta) (at <71e256980c424823a60822d6a2aa03cd>:0)
UnityEditor.UIElements.UXMLImporterImpl.Import (UnityEngine.UIElements.VisualTreeAsset& asset) (at <71e256980c424823a60822d6a2aa03cd>:0)
UnityEditor.UIElements.UIElementsViewImporter.OnImportAsset (UnityEditor.Experimental.AssetImporters.AssetImportContext args) (at <71e256980c424823a60822d6a2aa03cd>:0)
UnityEditor.Experimental.AssetImporters.ScriptedImporter.GenerateAssetData (UnityEditor.Experimental.AssetImporters.AssetImportContext ctx) (at <71e256980c424823a60822d6a2aa03cd>:0)

IOException : Could not find a part of the path "D:\Packages\com.unity.timeline\Editor\StyleSheets\Extensions\dark.uss".
IOException : Could not find a part of the path "D:\Packages\com.unity.timeline\Editor\StyleSheets\Extensions\light.uss".
IOException : Could not find a part of the path "D:\Packages\com.unity.collab-proxy\Editor\Resources\Styles\CollabHistoryLight.uss".
IOException : Could not find a part of the path "D:\Packages\com.unity.collab-proxy\Editor\Resources\Styles\CollabHistoryCommon.uss".
IOException : Could not find a part of the path "D:\Packages\com.unity.timeline\Editor\StyleSheets\Extensions\common.uss".