Thanks for providing me such detailed information especially on the troubleshooting steps you’ve performed with our Technical Support Team. I want to ensure you can open your company file seamlessly.
Now, let’s try some new steps to check if the problem possibly lies on the file or QuickBooks. To begin, open a sample file.
In the No Company Open window, click on the drop-down for Open a Sample File.
Then choose any from the list of sample company files.
If you’re able to open it without any errors, then repair your QuickBooks.
Before repairing the software, create a backup copy of the company file so you'll have a record of your previous transactions.
Click on Start and select Control Panel.
Select Programs and Features. If necessary, select Uninstall a program.
Choose QuickBooks in the list of programs and click on Uninstall/Change.
If prompted, click on Continue and Next.
Click on Finish and restart your computer if prompted.
Once done, let’s reopen your QuickBooks and make sure multi-user is set up correctly. For the detailed instructions, check out this article: Set up multi-user.
If you still get the same result, I recommend you give our support team another call. Just make sure to have your case number handy, so the agent can review the notes from your previous call and perform the troubleshooting steps from there.