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If none of the troubleshooting recommended in this thread has solved the problem of QuickBooks crashing when you try accessing multi-user mode, you'll want to continue getting in touch with our Customer Care team. They'll be able to pull up your account in a secure environment, conduct further research, and create an investigation ticket if necessary.

Detailed steps for reaching them can be found in my previous post.

You'll also be able to find many detailed resources about using QuickBooks in our help article archives.

Please don't hesitate to send a reply if there's any additional questions. Have a wonderful day!