When launching iRacing, a user may receive the following Unexpected Error window if something is preventing iRacing from reading or writing files in the user's ..\Documents\iRacing\ directory.
When this occurs, there will be no `main-ui.log` to send to support. To troubleshoot if this is the case, iRacing can be launched from the command line using the following steps.
Open a command prompt by clicking on Start, typing cmd and the selecting Command Prompt. 
At the command prompt change directory to where iRacing is installed and then enter the ui directory. Then launch the UI by typing iracingui.exe as seen in the example below. Even if the logs cannot be written to a file, they will be output in the command prompt. Below is an example of a successful launch.
An unsuccessful launch should provide information in the logs that indicate what error was encountered. Screenshot or copy and paste the text and send it Support.
C:\>cd "c:\Program Files (x86)\iRacing\ui"
c:\Program Files (x86)\iRacing\ui>iRacingUI.exe
c:\Program Files (x86)\iRacing\ui>
No local config found.
{"name":"iracing-electron","hostname":"WORKPC","pid":38072,"level":30,"msg":"GPU feature status {\n '2d_canvas': 'enabled',\n canvas_oop_rasterization: 'disabled_off',\n direct_rendering_display_compositor: 'disabled_off_ok',\n gpu_compositing: 'enabled',\n multiple_raster_threads: 'enabled_on',\n opengl: 'enabled_on',\n rasterization: 'enabled',\n raw_draw: 'disabled_off_ok',\n video_decode: 'enabled',\n video_encode: 'enabled',\n vulkan: 'disabled_off',\n webgl: 'enabled',\n webgl2: 'enabled',\n webgpu: 'disabled_off'\n}","time":"2023-11-16T20:55:49.793Z","v":0}
{"name":"iracing-electron","hostname":"WORKPC","pid":38072,"level":30,"msg":"status: Checking Credentials | Sim Inactive","time":"2023-11-16T20:55:51.636Z","v":0}
{"name":"iracing-electron","hostname":"WORKPC","pid":38072,"level":30,"msg":"status: Welcome to iRacing! | Sim Inactive","time":"2023-11-16T20:55:52.101Z","v":0}