If you're getting crashes when importing the SDK, try starting a new project. Import the VRCSDK first, then start bringing your assets back into the project one at a time. You can also try clicking "Detatch" in the Pipeline Manager on your World/Avatar descriptor, but keep in mind this will generate a new ID.
Still having issues after trying all that? Send us your Editor log! You can find the editor log here:
or just copy and paste this line into an Explorer window address bar:
Attach the files in this folder (Editor.log) to a ticket. You can create a ticket at our Helpdesk page. Please ensure that you select the Support category, attach any relevant files, and describe your issue as best as possible.